Difference between revisions of "University of South Carolina High School Math Contest/1993 Exam/Problems"

(Problem 6)
m (Problem 27: fix latex)
 
(5 intermediate revisions by 2 users not shown)
Line 2: Line 2:
 
If the width of a particular rectangle is doubled and the length is increased by 3, then the area is tripled. What is the length of the rectangle?
 
If the width of a particular rectangle is doubled and the length is increased by 3, then the area is tripled. What is the length of the rectangle?
  
<center><math> \mathrm{(A) \ } 1 \qquad \mathrm{(B) \ } 2 \qquad \mathrm{(C) \ } 3 \qquad \mathrm{(D) \ } 6 \qquad \mathrm{(E) \ } 9 </math></center>
+
<cmath> \mathrm{(A) \ } 1 \qquad \mathrm{(B) \ } 2 \qquad \mathrm{(C) \ } 3 \qquad \mathrm{(D) \ } 6 \qquad \mathrm{(E) \ } 9 </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 1|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 1|Solution]]
Line 9: Line 9:
 
Suppose the operation <math>\star</math> is defined by <math>a \star b = a+b+ab.</math> If <math>3\star x = 23,</math> then <math>x =</math>
 
Suppose the operation <math>\star</math> is defined by <math>a \star b = a+b+ab.</math> If <math>3\star x = 23,</math> then <math>x =</math>
  
<center><math> \mathrm{(A) \ } 2 \qquad \mathrm{(B) \ }3\qquad \mathrm{(C) \ }4 \qquad \mathrm{(D) \ }5 \qquad \mathrm{(E) \ }6  </math></center>
+
<cmath> \mathrm{(A) \ } 2 \qquad \mathrm{(B) \ }3\qquad \mathrm{(C) \ }4 \qquad \mathrm{(D) \ }5 \qquad \mathrm{(E) \ }6  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 2|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 2|Solution]]
Line 18: Line 18:
 
<center>[[Image:Usc93.3.PNG]]</center>
 
<center>[[Image:Usc93.3.PNG]]</center>
  
<center><math> \mathrm{(A) \ }\sqrt{3}-\frac{\pi}2 \qquad \mathrm{(B) \ } \frac 16 \qquad \mathrm{(C) \ }\frac 13 \qquad \mathrm{(D) \ } \frac{\sqrt{3}}2 - \frac{\pi}6 \qquad \mathrm{(E) \ } \frac{\pi}6 </math></center>
+
<cmath> \mathrm{(A) \ }\sqrt{3}-\frac{\pi}2 \qquad \mathrm{(B) \ } \frac 16 \qquad \mathrm{(C) \ }\frac 13 \qquad \mathrm{(D) \ } \frac{\sqrt{3}}2 - \frac{\pi}6 \qquad \mathrm{(E) \ } \frac{\pi}6 </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 3|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 3|Solution]]
Line 25: Line 25:
 
If <math>(1 + i)^{100}</math> is expanded and written in the form <math>a + bi</math> where <math>a</math> and <math>b</math> are real numbers, then <math>a =</math>
 
If <math>(1 + i)^{100}</math> is expanded and written in the form <math>a + bi</math> where <math>a</math> and <math>b</math> are real numbers, then <math>a =</math>
  
<center><math> \mathrm{(A) \ } -2^{50} \qquad \mathrm{(B) \ } 20^{50}  - \frac{100!}{50!50!} \qquad \mathrm{(C) \ } \frac{100!}{(25!)^2 50!} \qquad \mathrm{(D) \ } 100! \left(-\frac 1{50!50!} + \frac 1{25!75!}\right) \qquad \mathrm{(E) \ } 0 </math></center>
+
<cmath> \mathrm{(A) \ } -2^{50} \qquad \mathrm{(B) \ } 20^{50}  - \frac{100!}{50!50!} \qquad \mathrm{(C) \ } \frac{100!}{(25!)^2 50!} \qquad \mathrm{(D) \ } 100! \left(-\frac 1{50!50!} + \frac 1{25!75!}\right) \qquad \mathrm{(E) \ } 0</cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 4|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 4|Solution]]
Line 32: Line 32:
 
Suppose that <math>f</math> is a function with the property that for all <math>x</math> and <math>y, f(x + y) = f(x) + f(y) + 1</math> and <math>f(1) = 2.</math> What is the value of <math>f(3)</math>?
 
Suppose that <math>f</math> is a function with the property that for all <math>x</math> and <math>y, f(x + y) = f(x) + f(y) + 1</math> and <math>f(1) = 2.</math> What is the value of <math>f(3)</math>?
  
<center><math> \mathrm{(A) \ }4 \qquad \mathrm{(B) \ }5 \qquad \mathrm{(C) \ }6 \qquad \mathrm{(D) \ }7 \qquad \mathrm{(E) \ }8  </math></center>
+
<cmath> \mathrm{(A) \ }4 \qquad \mathrm{(B) \ }5 \qquad \mathrm{(C) \ }6 \qquad \mathrm{(D) \ }7 \qquad \mathrm{(E) \ }8  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 5|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 5|Solution]]
Line 48: Line 48:
 
<center>[[Image:Usc93.7.PNG]]</center>
 
<center>[[Image:Usc93.7.PNG]]</center>
  
<center><math> \mathrm{(A) \ }4.2 \qquad \mathrm{(B) \ }5 \qquad \mathrm{(C) \ }5.6 \qquad \mathrm{(D) \ }6.2  \qquad \mathrm{(E) \ }6.8  </math></center>
+
<cmath> \mathrm{(A) \ }4.2 \qquad \mathrm{(B) \ }5 \qquad \mathrm{(C) \ }5.6 \qquad \mathrm{(D) \ }6.2  \qquad \mathrm{(E) \ }6.8  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 7|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 7|Solution]]
Line 55: Line 55:
 
What is the coefficient of <math>x^3</math> in the expansion of  
 
What is the coefficient of <math>x^3</math> in the expansion of  
  
<center><math>(1 + x + x^2 + x^3 + x^4 + x^5 )^6? </math></center>
+
<cmath>(1 + x + x^2 + x^3 + x^4 + x^5 )^6? </cmath>
  
<center><math> \mathrm{(A) \ } 40 \qquad \mathrm{(B) \ }48 \qquad \mathrm{(C) \ }56 \qquad \mathrm{(D) \ }62 \qquad \mathrm{(E) \ } 64 </math></center>
+
<cmath> \mathrm{(A) \ } 40 \qquad \mathrm{(B) \ }48 \qquad \mathrm{(C) \ }56 \qquad \mathrm{(D) \ }62 \qquad \mathrm{(E) \ } 64 </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 8|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 8|Solution]]
Line 64: Line 64:
 
Suppose that <math>x</math> and <math>y</math> are integers such that <math>y > x > 1</math> and <math>y^2 - x^2 = 187</math>.  Then one possible value of <math>xy</math> is
 
Suppose that <math>x</math> and <math>y</math> are integers such that <math>y > x > 1</math> and <math>y^2 - x^2 = 187</math>.  Then one possible value of <math>xy</math> is
  
<center><math> \mathrm{(A) \ }30 \qquad \mathrm{(B) \ }36 \qquad \mathrm{(C) \ }40 \qquad \mathrm{(D) \ }42 \qquad \mathrm{(E) \ }54  </math></center>
+
<cmath> \mathrm{(A) \ }30 \qquad \mathrm{(B) \ }36 \qquad \mathrm{(C) \ }40 \qquad \mathrm{(D) \ }42 \qquad \mathrm{(E) \ }54  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 9|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 9|Solution]]
Line 71: Line 71:
 
<math>\arcsin(1/3) + \arccos(1/3) + \arctan(1/3) +  arccot(1/3) =</math>
 
<math>\arcsin(1/3) + \arccos(1/3) + \arctan(1/3) +  arccot(1/3) =</math>
  
<center><math> \mathrm{(A) \ }\pi \qquad \mathrm{(B) \ }\pi/2 \qquad \mathrm{(C) \ }\pi/3 \qquad \mathrm{(D) \ }2\pi/3 \qquad \mathrm{(E) \ }3/\pi/4  </math></center>
+
<cmath> \mathrm{(A) \ }\pi \qquad \mathrm{(B) \ }\pi/2 \qquad \mathrm{(C) \ }\pi/3 \qquad \mathrm{(D) \ }2\pi/3 \qquad \mathrm{(E) \ }3/\pi/4  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 10|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 10|Solution]]
Line 78: Line 78:
 
Suppose that 4 cards labeled 1 to 4 are placed randomly into 4 boxes also labeled 1 to 4, one card per box. What is the probability that no card gets placed into a box having the same label as the card?
 
Suppose that 4 cards labeled 1 to 4 are placed randomly into 4 boxes also labeled 1 to 4, one card per box. What is the probability that no card gets placed into a box having the same label as the card?
  
<center><math> \mathrm{(A) \ } 1/3 \qquad \mathrm{(B) \ }3/8 \qquad \mathrm{(C) \ }5/12 \qquad \mathrm{(D) \ } 1/2 \qquad \mathrm{(E) \ }9/16  </math></center>
+
<cmath> \mathrm{(A) \ } 1/3 \qquad \mathrm{(B) \ }3/8 \qquad \mathrm{(C) \ }5/12 \qquad \mathrm{(D) \ } 1/2 \qquad \mathrm{(E) \ }9/16  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 11|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 11|Solution]]
Line 85: Line 85:
 
If the equations <math> (1) x^2 + ax + b = 0</math> and <math> (2) x^2 + cx + d = 0 </math> have exactly one root in common, and <math> abcd\ne 0,</math> then the other root of equation <math> (2) </math> is  
 
If the equations <math> (1) x^2 + ax + b = 0</math> and <math> (2) x^2 + cx + d = 0 </math> have exactly one root in common, and <math> abcd\ne 0,</math> then the other root of equation <math> (2) </math> is  
  
<center><math> \mathrm{(A) \ }\frac{c-a}{b-d}d \qquad \mathrm{(B) \ }\frac{a+c}{b+d}d \qquad \mathrm{(C) \ }\frac{b+c}{a+d}c \qquad \mathrm{(D) \ }\frac{a-c}{b-d} \qquad \mathrm{(E) \ }\frac{a+c}{b-d}c  </math></center>
+
<cmath> \mathrm{(A) \ }\frac{c-a}{b-d}d \qquad \mathrm{(B) \ }\frac{a+c}{b+d}d \qquad \mathrm{(C) \ }\frac{b+c}{a+d}c \qquad \mathrm{(D) \ }\frac{a-c}{b-d} \qquad \mathrm{(E) \ }\frac{a+c}{b-d}c  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 12|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 12|Solution]]
Line 92: Line 92:
 
Suppose that <math>x</math> and <math>y</math> are numbers such that <math>\sin(x+y) = 0.3</math> and <math>\sin(x-y) = 0.5</math>.  Then <math> \sin (x)\cdot \cos (y) = </math>
 
Suppose that <math>x</math> and <math>y</math> are numbers such that <math>\sin(x+y) = 0.3</math> and <math>\sin(x-y) = 0.5</math>.  Then <math> \sin (x)\cdot \cos (y) = </math>
  
<center><math> \mathrm{(A) \ }0.1 \qquad \mathrm{(B) \ }0.3 \qquad \mathrm{(C) \ }0.4 \qquad \mathrm{(D) \ }0.5 \qquad \mathrm{(E) \ }0.6  </math></center>
+
<cmath> \mathrm{(A) \ }0.1 \qquad \mathrm{(B) \ }0.3 \qquad \mathrm{(C) \ }0.4 \qquad \mathrm{(D) \ }0.5 \qquad \mathrm{(E) \ }0.6  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 13|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 13|Solution]]
Line 103: Line 103:
 
For example, 8 1 5 7 2 3 9 4 6 would be such a permutation.
 
For example, 8 1 5 7 2 3 9 4 6 would be such a permutation.
  
<center><math> \mathrm{(A) \ }9\cdot 7! \qquad \mathrm{(B) \ } 8! \qquad \mathrm{(C) \ }5!4! \qquad \mathrm{(D) \ }8!4! \qquad \mathrm{(E) \ }8!+6!+4!  </math></center>
+
<cmath> \mathrm{(A) \ }9\cdot 7! \qquad \mathrm{(B) \ } 8! \qquad \mathrm{(C) \ }5!4! \qquad \mathrm{(D) \ }8!4! \qquad \mathrm{(E) \ }8!+6!+4!  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 14|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 14|Solution]]
Line 110: Line 110:
 
If we express the sum
 
If we express the sum
  
<center><math> \frac 1{3\cdot 5\cdot 7\cdot 11} + \frac 1{3\cdot 5\cdot 7\cdot 13} + \frac 1{3\cdot 5\cdot 11\cdot 13} + \frac 1{3\cdot 7\cdot 11\cdot 13} + \frac 1{5\cdot 7\cdot 11\cdot 13} </math></center>
+
<cmath> \frac 1{3\cdot 5\cdot 7\cdot 11} + \frac 1{3\cdot 5\cdot 7\cdot 13} + \frac 1{3\cdot 5\cdot 11\cdot 13} + \frac 1{3\cdot 7\cdot 11\cdot 13} + \frac 1{5\cdot 7\cdot 11\cdot 13} </cmath>
  
 
as a rational number in reduced form, then the denominator will be
 
as a rational number in reduced form, then the denominator will be
  
<center><math> \mathrm{(A) \ }15015 \qquad \mathrm{(B) \ }5005 \qquad \mathrm{(C) \ }455 \qquad \mathrm{(D) \ }385 \qquad \mathrm{(E) \ }91  </math></center>
+
<cmath> \mathrm{(A) \ }15015 \qquad \mathrm{(B) \ }5005 \qquad \mathrm{(C) \ }455 \qquad \mathrm{(D) \ }385 \qquad \mathrm{(E) \ }91  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 15|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 15|Solution]]
  
 
== Problem 16 ==
 
== Problem 16 ==
In the triangle below, <math>\displaystyle M, N, </math> and <math>P</math> are the midpoints of <math>BC, AB,</math> and <math>AC</math> respectively.  <math>CN</math> and <math>AM</math> intersect at <math>O</math>.  If the length of <math>CQ</math> is 4, then what is the length of <math>OQ</math>?
+
In the triangle below, <math>M, N, </math> and <math>P</math> are the midpoints of <math>BC, AB,</math> and <math>AC</math> respectively.  <math>CN</math> and <math>AM</math> intersect at <math>O</math>.  If the length of <math>CQ</math> is 4, then what is the length of <math>OQ</math>?
  
 
<center>[[Image:Usc93.16.PNG]]</center>
 
<center>[[Image:Usc93.16.PNG]]</center>
  
<center><math> \mathrm{(A) \ }1 \qquad \mathrm{(B) \ }4/3 \qquad \mathrm{(C) \ }\sqrt{2} \qquad \mathrm{(D) \ }3/2 \qquad \mathrm{(E) \ }2  </math></center>
+
<cmath> \mathrm{(A) \ }1 \qquad \mathrm{(B) \ }4/3 \qquad \mathrm{(C) \ }\sqrt{2} \qquad \mathrm{(D) \ }3/2 \qquad \mathrm{(E) \ }2  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 16|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 16|Solution]]
Line 130: Line 130:
 
Let <math>[x]</math> represent the greatest integer that is less than or equal to <math>x</math>.  For example, <math>[2.769]=2</math> and <math>[\pi]=3</math>.  Then what is the value of  
 
Let <math>[x]</math> represent the greatest integer that is less than or equal to <math>x</math>.  For example, <math>[2.769]=2</math> and <math>[\pi]=3</math>.  Then what is the value of  
  
<center><math> [\log_2 2] + [\log_2 3] + [\log_2 4] + \cdots + [\log_2 99] + [\log_2 100] ?</math></center>
+
<cmath> [\log_2 2] + [\log_2 3] + [\log_2 4] + \cdots + [\log_2 99] + [\log_2 100] ?</cmath>
  
<center><math> \mathrm{(A) \ } 480 \qquad \mathrm{(B) \ }481 \qquad \mathrm{(C) \ }482 \qquad \mathrm{(D) \ }483 \qquad \mathrm{(E) \ }484  </math></center>
+
<cmath> \mathrm{(A) \ } 480 \qquad \mathrm{(B) \ }481 \qquad \mathrm{(C) \ }482 \qquad \mathrm{(D) \ }483 \qquad \mathrm{(E) \ }484  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 17|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 17|Solution]]
Line 139: Line 139:
 
The minimum value of the function
 
The minimum value of the function
  
<center><math>\displaystyle f(x) = \frac{\sin (x)}{\sqrt{1 - \cos^2 (x)}} + \frac{\cos(x)}{\sqrt{1 - \sin^2 (x) }} + \frac{\tan(x)}{\sqrt{\sec^2 (x) - 1}} + \frac{\cot (x)}{\sqrt{\csc^2 (x) - 1}}</math></center>  
+
<cmath>f(x) = \frac{\sin (x)}{\sqrt{1 - \cos^2 (x)}} + \frac{\cos(x)}{\sqrt{1 - \sin^2 (x) }} + \frac{\tan(x)}{\sqrt{\sec^2 (x) - 1}} + \frac{\cot (x)}{\sqrt{\csc^2 (x) - 1}}</cmath>  
  
 
as <math>x</math> varies over all numbers in the largest possible domain of <math>f</math>, is  
 
as <math>x</math> varies over all numbers in the largest possible domain of <math>f</math>, is  
  
<center><math> \mathrm{(A) \ }-4 \qquad \mathrm{(B) \ }-2 \qquad \mathrm{(C) \ }0 \qquad \mathrm{(D) \ }2 \qquad \mathrm{(E) \ }4  </math></center>
+
<cmath> \mathrm{(A) \ }-4 \qquad \mathrm{(B) \ }-2 \qquad \mathrm{(C) \ }0 \qquad \mathrm{(D) \ }2 \qquad \mathrm{(E) \ }4  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 18|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 18|Solution]]
Line 152: Line 152:
 
<center>[[Image:Usc93.19.PNG]]</center>
 
<center>[[Image:Usc93.19.PNG]]</center>
  
<center><math> \mathrm{(A) \ }24 \qquad \mathrm{(B) \ }72 \qquad \mathrm{(C) \ }84 \qquad \mathrm{(D) \ }96 \qquad \mathrm{(E) \ }108  </math></center>
+
<cmath> \mathrm{(A) \ }24 \qquad \mathrm{(B) \ }72 \qquad \mathrm{(C) \ }84 \qquad \mathrm{(D) \ }96 \qquad \mathrm{(E) \ }108  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 19|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 19|Solution]]
Line 159: Line 159:
 
Let <math>A_1, A_2, \ldots , A_{63}</math> be the 63 nonempty subsets of <math>\{ 1,2,3,4,5,6 \}</math>.  For each of these sets <math>A_i</math>, let <math>\pi(A_i)</math> denote the product of all the elements in <math>A_i</math>.  Then what is the value of <math>\pi(A_1)+\pi(A_2)+\cdots+\pi(A_{63})</math>?
 
Let <math>A_1, A_2, \ldots , A_{63}</math> be the 63 nonempty subsets of <math>\{ 1,2,3,4,5,6 \}</math>.  For each of these sets <math>A_i</math>, let <math>\pi(A_i)</math> denote the product of all the elements in <math>A_i</math>.  Then what is the value of <math>\pi(A_1)+\pi(A_2)+\cdots+\pi(A_{63})</math>?
  
<center><math> \mathrm{(A) \ }5003 \qquad \mathrm{(B) \ }5012 \qquad \mathrm{(C) \ }5039 \qquad \mathrm{(D) \ }5057 \qquad \mathrm{(E) \ }5093  </math></center>
+
<cmath> \mathrm{(A) \ }5003 \qquad \mathrm{(B) \ }5012 \qquad \mathrm{(C) \ }5039 \qquad \mathrm{(D) \ }5057 \qquad \mathrm{(E) \ }5093  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 20|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 20|Solution]]
Line 166: Line 166:
 
Suppose that each pair of eight tennis players either played exactly one game last week or did not play at all. Each player participated in all but 12 games. How many games were played among the eight players?
 
Suppose that each pair of eight tennis players either played exactly one game last week or did not play at all. Each player participated in all but 12 games. How many games were played among the eight players?
  
<center><math> \mathrm{(A) \ }10 \qquad \mathrm{(B) \ }12 \qquad \mathrm{(C) \ }14 \qquad \mathrm{(D) \ }16 \qquad \mathrm{(E) \ }18  </math></center>
+
<cmath> \mathrm{(A) \ }10 \qquad \mathrm{(B) \ }12 \qquad \mathrm{(C) \ }14 \qquad \mathrm{(D) \ }16 \qquad \mathrm{(E) \ }18  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 21|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 21|Solution]]
Line 173: Line 173:
 
Let  
 
Let  
  
<center><math> A = \left( 1 + \frac 12 + \frac 14 + \frac 18 + \frac 1{16} \right) \left( 1 + \frac 13 + \frac 19\right) \left( 1 + \frac 15\right) \left( 1 + \frac 17\right) \left( 1 + \frac 1{11} \right) \left( 1 + \frac 1{13}\right), </math></center>
+
<cmath> A = \left( 1 + \frac 12 + \frac 14 + \frac 18 + \frac 1{16} \right) \left( 1 + \frac 13 + \frac 19\right) \left( 1 + \frac 15\right) \left( 1 + \frac 17\right) \left( 1 + \frac 1{11} \right) \left( 1 + \frac 1{13}\right), </cmath>
  
<center> <math> B = \left( 1 - \frac 12\right)^{-1} \left( 1 - \frac 13 \right)^{-1} \left(1 - \frac 15\right)^{-1} \left(1 - \frac 17\right)^{-1} \left(1-\frac 1{11}\right)^{-1} \left(1 - \frac 1{13}\right)^{-1}, </math></center>
+
<cmath>B = \left( 1 - \frac 12\right)^{-1} \left( 1 - \frac 13 \right)^{-1} \left(1 - \frac 15\right)^{-1} \left(1 - \frac 17\right)^{-1} \left(1-\frac 1{11}\right)^{-1} \left(1 - \frac 1{13}\right)^{-1}, </cmath>
  
 
and
 
and
  
<center><math> C = 1 + \frac 12 + \frac 13 + \frac 14 + \frac 15 + \frac 16 + \frac 17 + \frac 18 + \frac 19 + \frac 1{10} + \frac 1{11} + \frac 1{12} + \frac 1{13} + \frac 1{14} + \frac 1{15} +\frac 1{16}. </math></center>
+
<cmath> C = 1 + \frac 12 + \frac 13 + \frac 14 + \frac 15 + \frac 16 + \frac 17 + \frac 18 + \frac 19 + \frac 1{10} + \frac 1{11} + \frac 1{12} + \frac 1{13} + \frac 1{14} + \frac 1{15} +\frac 1{16}. </cmath>
  
 
Then which of the following inequalities is true?
 
Then which of the following inequalities is true?
  
<center><math> \mathrm{(A) \ } A > B > C \qquad \mathrm{(B) \ } B > A  > C \qquad \mathrm{(C) \ } C > B > A \qquad \mathrm{(D) \ } C > A > B \qquad \mathrm{(E) \ } B > C > A  </math></center>
+
<cmath> \mathrm{(A) \ } A > B > C \qquad \mathrm{(B) \ } B > A  > C \qquad \mathrm{(C) \ } C > B > A \qquad \mathrm{(D) \ } C > A > B \qquad \mathrm{(E) \ } B > C > A  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 22|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 22|Solution]]
Line 190: Line 190:
 
The relation between the sets
 
The relation between the sets
  
<center><math> M = \{ 12 m + 8 n + 4 l: m,n,l \rm{ \ are \ } \rm{integers}\} </math></center>
+
<cmath> M = \{ 12 m + 8 n + 4 l: m,n,l \rm{ \ are \ } \rm{integers}\} </cmath>
  
 
and
 
and
  
<center><math> N= \{ 20 p + 16q + 12r: p,q,r \rm{ \ are \ } \rm{integers}\} </math></center>
+
<cmath> N= \{ 20 p + 16q + 12r: p,q,r \rm{ \ are \ } \rm{integers}\} </cmath>
  
 
is
 
is
<center><math> \mathrm{(A) \ } M\subset N \qquad \mathrm{(B) \ } N\subset M \qquad \mathrm{(C) \ } M\cup N = \{0\} \qquad \mathrm{(D) \ }60244 \rm{ \ is \ } \rm{in \ } M \rm{ \ but \ } \rm{not \ } \rm{in \ } N \qquad \mathrm{(E) \ } M=N  </math></center>
+
<cmath> \mathrm{(A) \ } M\subset N \qquad \mathrm{(B) \ } N\subset M \qquad \mathrm{(C) \ } M\cup N = \{0\} \qquad \mathrm{(D) \ }60244 \rm{ \ is \ } \rm{in \ } M \rm{ \ but \ } \rm{not \ } \rm{in \ } N \qquad \mathrm{(E) \ } M=N  </cmath>
  
  
Line 205: Line 205:
 
If <math>f(x) = \frac{1 + x}{1 - 3x}, f_1(x) = f(f(x)), f_2(x) = f(f_1(x)),</math> and in general <math>f_n(x) = f(f_{n-1}(x)),</math> then <math>f_{1993}(3)=</math>
 
If <math>f(x) = \frac{1 + x}{1 - 3x}, f_1(x) = f(f(x)), f_2(x) = f(f_1(x)),</math> and in general <math>f_n(x) = f(f_{n-1}(x)),</math> then <math>f_{1993}(3)=</math>
  
<center><math> \mathrm{(A) \ }3 \qquad \mathrm{(B) \ }1993 \qquad \mathrm{(C) \ }\frac 12 \qquad \mathrm{(D) \ }\frac 15 \qquad \mathrm{(E) \ } -2^{-1993}  </math></center>
+
<cmath> \mathrm{(A) \ }3 \qquad \mathrm{(B) \ }1993 \qquad \mathrm{(C) \ }\frac 12 \qquad \mathrm{(D) \ }\frac 15 \qquad \mathrm{(E) \ } -2^{-1993}  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 24|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 24|Solution]]
Line 212: Line 212:
 
What is the center of the circle passing through the point <math>(6,0)</math> and tangent to the circle <math>x^2 + y^2 = 4</math> at <math>(0,2)</math>? (Two circles are tangent at a point <math>P</math> if they intersect at <math>P</math> and at no other point.)
 
What is the center of the circle passing through the point <math>(6,0)</math> and tangent to the circle <math>x^2 + y^2 = 4</math> at <math>(0,2)</math>? (Two circles are tangent at a point <math>P</math> if they intersect at <math>P</math> and at no other point.)
  
<center><math> \mathrm{(A) \ }(0,-6) \qquad \mathrm{(B) \ } (1,-9) \qquad \mathrm{(C) \ } (-1,-9) \qquad \mathrm{(D) \ } (0,-9) \qquad \mathrm{(E) \ } \rm{none \ } \rm{of \ } \rm{these} </math></center>
+
<cmath> \mathrm{(A) \ }(0,-6) \qquad \mathrm{(B) \ } (1,-9) \qquad \mathrm{(C) \ } (-1,-9) \qquad \mathrm{(D) \ } (0,-9) \qquad \mathrm{(E) \ } \rm{none \ } \rm{of \ } \rm{these} </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 25|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 25|Solution]]
Line 219: Line 219:
 
Let <math>n=1667</math>.  Then the first nonzero digit in the decimal expansion of <math>\sqrt{n^2 + 1} - n</math> is  
 
Let <math>n=1667</math>.  Then the first nonzero digit in the decimal expansion of <math>\sqrt{n^2 + 1} - n</math> is  
  
<center><math> \mathrm{(A) \ }1 \qquad \mathrm{(B) \ }2 \qquad \mathrm{(C) \ }3 \qquad \mathrm{(D) \ }4 \qquad \mathrm{(E) \ }5  </math></center>
+
<cmath> \mathrm{(A) \ }1 \qquad \mathrm{(B) \ }2 \qquad \mathrm{(C) \ }3 \qquad \mathrm{(D) \ }4 \qquad \mathrm{(E) \ }5  </cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 26|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 26|Solution]]
Line 226: Line 226:
 
Suppose <math>\triangle ABC</math> is a triangle with area 24 and that there is a point <math>P</math> inside <math>\triangle ABC</math> which is distance 2 from each of the sides of <math>\triangle ABC</math>.  What is the perimeter of <math>\triangle ABC</math>?
 
Suppose <math>\triangle ABC</math> is a triangle with area 24 and that there is a point <math>P</math> inside <math>\triangle ABC</math> which is distance 2 from each of the sides of <math>\triangle ABC</math>.  What is the perimeter of <math>\triangle ABC</math>?
  
<center><math>
+
<cmath> \mathrm{(A) \ } 12 \qquad \mathrm{(B) \ }24 \qquad \mathrm{(C) \ }36 \qquad \mathrm{(D) \ }12\sqrt{2} \qquad \mathrm{(E) \ }12\sqrt{3}  </cmath>
\mathrm{(A) \ } 12 \qquad \mathrm{(B) \ }24 \qquad \mathrm{(C) \ }36 \qquad \mathrm{(D) \ }12\sqrt{2} \qquad \mathrm{(E) \ }12\sqrt{3}  </math></center>
 
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 27|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 27|Solution]]
Line 249: Line 248:
 
If the sides of a triangle have lengths 2, 3, and 4, what is the radius of the circle circumscribing the triangle?
 
If the sides of a triangle have lengths 2, 3, and 4, what is the radius of the circle circumscribing the triangle?
  
<center><math>
+
<cmath>\mathrm{(A)}\quad 2
\mathrm{(A) \ } 2
+
\quad \mathrm{(B) }\quad 8/\sqrt{15}  
\qquad \mathrm{(B) \ } 8/\sqrt{15}  
+
\quad \mathrm{(C) }\quad 5/2
\qquad \mathrm{(C) \ } 5/2
+
\quad \mathrm{(D) }\quad \sqrt{6}
\qquad \mathrm{(D) \ } \sqrt{6}
+
\quad \mathrm{(E) }\quad (\sqrt{6} + 1)/2</cmath>
\qquad \mathrm{(E) \ } (\sqrt{6} + 1)/2
 
</math></center>
 
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 29|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 29|Solution]]
  
 
== Problem 30 ==
 
== Problem 30 ==
<center><math> \frac 1{1\cdot 2\cdot 3\cdot 4} + \frac 1{2\cdot 3\cdot 4\cdot 5} + \frac 1{3\cdot 4\cdot 5\cdot 6} + \cdots + \frac 1{28\cdot 29\cdot 30\cdot 31} = </math></center>
+
<cmath> \frac 1{1\cdot 2\cdot 3\cdot 4} + \frac 1{2\cdot 3\cdot 4\cdot 5} + \frac 1{3\cdot 4\cdot 5\cdot 6} + \cdots + \frac 1{28\cdot 29\cdot 30\cdot 31} = </cmath>
  
  
<center><math> \mathrm{(A) \ }1/18 \qquad \mathrm{(B) \ }1/21 \qquad \mathrm{(C) \ }4/93 \qquad \mathrm{(D) \ }128/2505 \qquad \mathrm{(E) \ }  749/13485</math></center>
+
<cmath> \mathrm{(A) \ }1/18 \qquad \mathrm{(B) \ }1/21 \qquad \mathrm{(C) \ }4/93 \qquad \mathrm{(D) \ }128/2505 \qquad \mathrm{(E) \ }  749/13485</cmath>
  
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 30|Solution]]
 
[[University of South Carolina High School Math Contest/1993 Exam/Problem 30|Solution]]

Latest revision as of 22:03, 26 October 2018

Problem 1

If the width of a particular rectangle is doubled and the length is increased by 3, then the area is tripled. What is the length of the rectangle?

\[\mathrm{(A) \ } 1 \qquad \mathrm{(B) \ } 2 \qquad \mathrm{(C) \ } 3 \qquad \mathrm{(D) \ } 6 \qquad \mathrm{(E) \ } 9\]

Solution

Problem 2

Suppose the operation $\star$ is defined by $a \star b = a+b+ab.$ If $3\star x = 23,$ then $x =$

\[\mathrm{(A) \ } 2 \qquad \mathrm{(B) \ }3\qquad \mathrm{(C) \ }4 \qquad \mathrm{(D) \ }5 \qquad \mathrm{(E) \ }6\]

Solution

Problem 3

If 3 circles of radius 1 are mutually tangent as shown, what is the area of the gap they enclose?

Usc93.3.PNG

\[\mathrm{(A) \ }\sqrt{3}-\frac{\pi}2 \qquad \mathrm{(B) \ } \frac 16 \qquad \mathrm{(C) \ }\frac 13 \qquad \mathrm{(D) \ } \frac{\sqrt{3}}2 - \frac{\pi}6 \qquad \mathrm{(E) \ } \frac{\pi}6\]

Solution

Problem 4

If $(1 + i)^{100}$ is expanded and written in the form $a + bi$ where $a$ and $b$ are real numbers, then $a =$

\[\mathrm{(A) \ } -2^{50} \qquad \mathrm{(B) \ } 20^{50}  - \frac{100!}{50!50!} \qquad \mathrm{(C) \ } \frac{100!}{(25!)^2 50!} \qquad \mathrm{(D) \ } 100! \left(-\frac 1{50!50!} + \frac 1{25!75!}\right) \qquad \mathrm{(E) \ } 0\]

Solution

Problem 5

Suppose that $f$ is a function with the property that for all $x$ and $y, f(x + y) = f(x) + f(y) + 1$ and $f(1) = 2.$ What is the value of $f(3)$?

\[\mathrm{(A) \ }4 \qquad \mathrm{(B) \ }5 \qquad \mathrm{(C) \ }6 \qquad \mathrm{(D) \ }7 \qquad \mathrm{(E) \ }8\]

Solution

Problem 6

After a $p \%$ price reduction, what increase does it take to restore the original price?

\[\mathrm{(A) \ }p\%  \qquad \mathrm{(B) \ }\frac p{1-p}\% \qquad \mathrm{(C) \ } (100-p)\% \qquad \mathrm{(D) \ } \frac{100p}{100+p}\% \qquad \mathrm{(E) \ } \frac{100p}{100-p}\%\]

Solution

Problem 7

Each card below covers up a number. The number written below each card is the sum of all the numbers covered by all of the other cards. What is the sum of all of the hidden numbers?

Usc93.7.PNG

\[\mathrm{(A) \ }4.2 \qquad \mathrm{(B) \ }5 \qquad \mathrm{(C) \ }5.6 \qquad \mathrm{(D) \ }6.2  \qquad \mathrm{(E) \ }6.8\]

Solution

Problem 8

What is the coefficient of $x^3$ in the expansion of

\[(1 + x + x^2 + x^3 + x^4 + x^5 )^6?\]

\[\mathrm{(A) \ } 40 \qquad \mathrm{(B) \ }48 \qquad \mathrm{(C) \ }56 \qquad \mathrm{(D) \ }62 \qquad \mathrm{(E) \ } 64\]

Solution

Problem 9

Suppose that $x$ and $y$ are integers such that $y > x > 1$ and $y^2 - x^2 = 187$. Then one possible value of $xy$ is

\[\mathrm{(A) \ }30 \qquad \mathrm{(B) \ }36 \qquad \mathrm{(C) \ }40 \qquad \mathrm{(D) \ }42 \qquad \mathrm{(E) \ }54\]

Solution

Problem 10

$\arcsin(1/3) + \arccos(1/3) + \arctan(1/3) +  arccot(1/3) =$

\[\mathrm{(A) \ }\pi \qquad \mathrm{(B) \ }\pi/2 \qquad \mathrm{(C) \ }\pi/3 \qquad \mathrm{(D) \ }2\pi/3 \qquad \mathrm{(E) \ }3/\pi/4\]

Solution

Problem 11

Suppose that 4 cards labeled 1 to 4 are placed randomly into 4 boxes also labeled 1 to 4, one card per box. What is the probability that no card gets placed into a box having the same label as the card?

\[\mathrm{(A) \ } 1/3 \qquad \mathrm{(B) \ }3/8 \qquad \mathrm{(C) \ }5/12 \qquad \mathrm{(D) \ } 1/2 \qquad \mathrm{(E) \ }9/16\]

Solution

Problem 12

If the equations $(1) x^2 + ax + b = 0$ and $(2) x^2 + cx + d = 0$ have exactly one root in common, and $abcd\ne 0,$ then the other root of equation $(2)$ is

\[\mathrm{(A) \ }\frac{c-a}{b-d}d \qquad \mathrm{(B) \ }\frac{a+c}{b+d}d \qquad \mathrm{(C) \ }\frac{b+c}{a+d}c \qquad \mathrm{(D) \ }\frac{a-c}{b-d} \qquad \mathrm{(E) \ }\frac{a+c}{b-d}c\]

Solution

Problem 13

Suppose that $x$ and $y$ are numbers such that $\sin(x+y) = 0.3$ and $\sin(x-y) = 0.5$. Then $\sin (x)\cdot \cos (y) =$

\[\mathrm{(A) \ }0.1 \qquad \mathrm{(B) \ }0.3 \qquad \mathrm{(C) \ }0.4 \qquad \mathrm{(D) \ }0.5 \qquad \mathrm{(E) \ }0.6\]

Solution

Problem 14

How many permutations of 1, 2, 3, 4, 5, 6, 7, 8, 9 have:

  • 1 appearing somewhere to the left of 2,
  • 3 somewhere to the left of 4, and
  • 5 somewhere to the left of 6?

For example, 8 1 5 7 2 3 9 4 6 would be such a permutation.

\[\mathrm{(A) \ }9\cdot 7! \qquad \mathrm{(B) \ } 8! \qquad \mathrm{(C) \ }5!4! \qquad \mathrm{(D) \ }8!4! \qquad \mathrm{(E) \ }8!+6!+4!\]

Solution

Problem 15

If we express the sum

\[\frac 1{3\cdot 5\cdot 7\cdot 11} + \frac 1{3\cdot 5\cdot 7\cdot 13} + \frac 1{3\cdot 5\cdot 11\cdot 13} + \frac 1{3\cdot 7\cdot 11\cdot 13} + \frac 1{5\cdot 7\cdot 11\cdot 13}\]

as a rational number in reduced form, then the denominator will be

\[\mathrm{(A) \ }15015 \qquad \mathrm{(B) \ }5005 \qquad \mathrm{(C) \ }455 \qquad \mathrm{(D) \ }385 \qquad \mathrm{(E) \ }91\]

Solution

Problem 16

In the triangle below, $M, N,$ and $P$ are the midpoints of $BC, AB,$ and $AC$ respectively. $CN$ and $AM$ intersect at $O$. If the length of $CQ$ is 4, then what is the length of $OQ$?

Usc93.16.PNG

\[\mathrm{(A) \ }1 \qquad \mathrm{(B) \ }4/3 \qquad \mathrm{(C) \ }\sqrt{2} \qquad \mathrm{(D) \ }3/2 \qquad \mathrm{(E) \ }2\]

Solution

Problem 17

Let $[x]$ represent the greatest integer that is less than or equal to $x$. For example, $[2.769]=2$ and $[\pi]=3$. Then what is the value of

\[[\log_2 2] + [\log_2 3] + [\log_2 4] + \cdots + [\log_2 99] + [\log_2 100] ?\]

\[\mathrm{(A) \ } 480 \qquad \mathrm{(B) \ }481 \qquad \mathrm{(C) \ }482 \qquad \mathrm{(D) \ }483 \qquad \mathrm{(E) \ }484\]

Solution

Problem 18

The minimum value of the function

\[f(x) = \frac{\sin (x)}{\sqrt{1 - \cos^2 (x)}} + \frac{\cos(x)}{\sqrt{1 - \sin^2 (x) }} + \frac{\tan(x)}{\sqrt{\sec^2 (x) - 1}} + \frac{\cot (x)}{\sqrt{\csc^2 (x) - 1}}\]

as $x$ varies over all numbers in the largest possible domain of $f$, is

\[\mathrm{(A) \ }-4 \qquad \mathrm{(B) \ }-2 \qquad \mathrm{(C) \ }0 \qquad \mathrm{(D) \ }2 \qquad \mathrm{(E) \ }4\]

Solution

Problem 19

In the figure below, there are 4 distinct dots $A, B, C,$ and $D$, joined by edges. Each dot is to be colored either red, blue, green, or yellow. No two dots joined by an edge are to be colored with the same color. How many completed colorings are possible?

Usc93.19.PNG

\[\mathrm{(A) \ }24 \qquad \mathrm{(B) \ }72 \qquad \mathrm{(C) \ }84 \qquad \mathrm{(D) \ }96 \qquad \mathrm{(E) \ }108\]

Solution

Problem 20

Let $A_1, A_2, \ldots , A_{63}$ be the 63 nonempty subsets of $\{ 1,2,3,4,5,6 \}$. For each of these sets $A_i$, let $\pi(A_i)$ denote the product of all the elements in $A_i$. Then what is the value of $\pi(A_1)+\pi(A_2)+\cdots+\pi(A_{63})$?

\[\mathrm{(A) \ }5003 \qquad \mathrm{(B) \ }5012 \qquad \mathrm{(C) \ }5039 \qquad \mathrm{(D) \ }5057 \qquad \mathrm{(E) \ }5093\]

Solution

Problem 21

Suppose that each pair of eight tennis players either played exactly one game last week or did not play at all. Each player participated in all but 12 games. How many games were played among the eight players?

\[\mathrm{(A) \ }10 \qquad \mathrm{(B) \ }12 \qquad \mathrm{(C) \ }14 \qquad \mathrm{(D) \ }16 \qquad \mathrm{(E) \ }18\]

Solution

Problem 22

Let

\[A = \left( 1 + \frac 12 + \frac 14 + \frac 18 + \frac 1{16} \right) \left( 1 + \frac 13 + \frac 19\right) \left( 1 + \frac 15\right) \left( 1 + \frac 17\right) \left( 1 + \frac 1{11} \right) \left( 1 + \frac 1{13}\right),\]

\[B = \left( 1 - \frac 12\right)^{-1} \left( 1 - \frac 13 \right)^{-1} \left(1 - \frac 15\right)^{-1} \left(1 - \frac 17\right)^{-1} \left(1-\frac 1{11}\right)^{-1} \left(1 - \frac 1{13}\right)^{-1},\]

and

\[C = 1 + \frac 12 + \frac 13 + \frac 14 + \frac 15 + \frac 16 + \frac 17 + \frac 18 + \frac 19 + \frac 1{10} + \frac 1{11} + \frac 1{12} + \frac 1{13} + \frac 1{14} + \frac 1{15} +\frac 1{16}.\]

Then which of the following inequalities is true?

\[\mathrm{(A) \ } A > B > C \qquad \mathrm{(B) \ } B > A  > C \qquad \mathrm{(C) \ } C > B > A \qquad \mathrm{(D) \ } C > A > B \qquad \mathrm{(E) \ } B > C > A\]

Solution

Problem 23

The relation between the sets

\[M = \{ 12 m + 8 n + 4 l: m,n,l \rm{ \ are \ } \rm{integers}\}\]

and

\[N= \{ 20 p + 16q + 12r: p,q,r \rm{ \ are \ } \rm{integers}\}\]

is \[\mathrm{(A) \ } M\subset N \qquad \mathrm{(B) \ } N\subset M \qquad \mathrm{(C) \ } M\cup N = \{0\} \qquad \mathrm{(D) \ }60244 \rm{ \ is \ } \rm{in \ } M \rm{ \ but \ } \rm{not \ } \rm{in \ } N \qquad \mathrm{(E) \ } M=N\]


Solution

Problem 24

If $f(x) = \frac{1 + x}{1 - 3x}, f_1(x) = f(f(x)), f_2(x) = f(f_1(x)),$ and in general $f_n(x) = f(f_{n-1}(x)),$ then $f_{1993}(3)=$

\[\mathrm{(A) \ }3 \qquad \mathrm{(B) \ }1993 \qquad \mathrm{(C) \ }\frac 12 \qquad \mathrm{(D) \ }\frac 15 \qquad \mathrm{(E) \ } -2^{-1993}\]

Solution

Problem 25

What is the center of the circle passing through the point $(6,0)$ and tangent to the circle $x^2 + y^2 = 4$ at $(0,2)$? (Two circles are tangent at a point $P$ if they intersect at $P$ and at no other point.)

\[\mathrm{(A) \ }(0,-6) \qquad \mathrm{(B) \ } (1,-9) \qquad \mathrm{(C) \ } (-1,-9) \qquad \mathrm{(D) \ } (0,-9) \qquad \mathrm{(E) \ } \rm{none \ } \rm{of \ } \rm{these}\]

Solution

Problem 26

Let $n=1667$. Then the first nonzero digit in the decimal expansion of $\sqrt{n^2 + 1} - n$ is

\[\mathrm{(A) \ }1 \qquad \mathrm{(B) \ }2 \qquad \mathrm{(C) \ }3 \qquad \mathrm{(D) \ }4 \qquad \mathrm{(E) \ }5\]

Solution

Problem 27

Suppose $\triangle ABC$ is a triangle with area 24 and that there is a point $P$ inside $\triangle ABC$ which is distance 2 from each of the sides of $\triangle ABC$. What is the perimeter of $\triangle ABC$?

\[\mathrm{(A) \ } 12 \qquad \mathrm{(B) \ }24 \qquad \mathrm{(C) \ }36 \qquad \mathrm{(D) \ }12\sqrt{2} \qquad \mathrm{(E) \ }12\sqrt{3}\]

Solution

Problem 28

Suppose $\triangle ABC$ is a triangle with 3 acute angles $A, B,$ and $C$. Then the point $( \cos B - \sin A, \sin B - \cos A)$

(A) can be in the 1st quadrant and can be in the 2nd quadrant only

(B) can be in the 3rd quadrant and can be in the 4th quadrant only

(C) can be in the 2nd quadrant and can be in the 3rd quadrant only

(D) can be in the 2nd quadrant only

(E) can be in any of the 4 quadrants

Solution

Problem 29

If the sides of a triangle have lengths 2, 3, and 4, what is the radius of the circle circumscribing the triangle?

\[\mathrm{(A)}\quad 2 \quad \mathrm{(B)  }\quad 8/\sqrt{15}  \quad \mathrm{(C) }\quad 5/2 \quad \mathrm{(D) }\quad \sqrt{6} \quad \mathrm{(E) }\quad  (\sqrt{6} + 1)/2\]

Solution

Problem 30

\[\frac 1{1\cdot 2\cdot 3\cdot 4} + \frac 1{2\cdot 3\cdot 4\cdot 5} + \frac 1{3\cdot 4\cdot 5\cdot 6} + \cdots + \frac 1{28\cdot 29\cdot 30\cdot 31} =\]


\[\mathrm{(A) \ }1/18 \qquad \mathrm{(B) \ }1/21 \qquad \mathrm{(C) \ }4/93 \qquad \mathrm{(D) \ }128/2505 \qquad \mathrm{(E) \ }  749/13485\]

Solution

See also