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Difference between revisions of "1998 AHSME Problems"

m (Hmmm... asy doesn't work... oh well.)
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{{AHSME Problems
 +
|year = 1998
 +
}}
 
== Problem 1 ==
 
== Problem 1 ==
−
Each of the sides of five congruent rectangles is labeled with an integer, as shown above. These five rectangles are placed, without rotating or reflecting, in positions <math>I</math> through <math>V</math> so that the labels on coincident sides are equal.
+
Each of the sides of five congruent rectangles is labeled with an integer. In rectangle A, <math>w = 4, x = 1, y = 6, z = 9</math>. In rectangle B, <math>w = 1, x = 0, y = 3, z = 6</math>. In rectangle C, <math>w = 3, x = 8, y = 5, z = 2</math>. In rectangle D, <math>w = 7, x = 5, y = 4, z = 8</math>. In rectangle E, <math>w = 9, x = 2, y = 7, z = 0</math>. These five rectangles are placed, without rotating or reflecting, in position as below. Which of the rectangle is the top leftmost one?
  
−
{{image}}
+
<center><asy>
−
 
+
draw((0,5)--(0,7)--(3,7)--(3,5)--cycle);
−
 
+
draw((0,4)--(9,4)--(9,2)--(6,2)--(6,0)--(0,0)--cycle);
−
Which of the rectangles is in position <math>I</math>?
+
draw((3,0)--(3,4));draw((6,2)--(6,4));draw((0,2)--(6,2));
 +
label("$w$",(0,6),(-1,0));label("$x$",(1.5,7),(0,1));label("$y$",(3,6),(1,0));label("$z$",(1.5,5),(0,-1));
 +
</asy></center>
  
 
<math> \mathrm{(A)\ } A \qquad \mathrm{(B) \ }B \qquad \mathrm{(C) \  } C \qquad \mathrm{(D) \  } D \qquad \mathrm{(E) \  }E  </math>
 
<math> \mathrm{(A)\ } A \qquad \mathrm{(B) \ }B \qquad \mathrm{(C) \  } C \qquad \mathrm{(D) \  } D \qquad \mathrm{(E) \  }E  </math>
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If <math>\texttt{a,b,}</math> and <math>\texttt{c}</math> are digits for which
 
If <math>\texttt{a,b,}</math> and <math>\texttt{c}</math> are digits for which
  
−
<center><math>\begin{tabular}{r}&\ \texttt{7 a 2}\\ &- \texttt{4 8 b} \\  
+
<cmath>\begin{array}{rccc}&\ \texttt{7}& \texttt{a}&\texttt{2}\\ -&\ \texttt{4}&\texttt{8}&\texttt{b} \\  
 
\hline  
 
\hline  
−
&\ \texttt{c 7 3} \end{tabular}</math></center>
+
&\ \texttt{c}&\texttt{7}& \texttt{3} \end{array}</cmath>
  
 
then <math>\texttt{a+b+c =}</math>
 
then <math>\texttt{a+b+c =}</math>
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A square with sides of length <math>1</math> is divided into two congruent trapezoids and a pentagon, which have equal areas, by joining the center of the square with points on three of the sides, as shown. Find <math>x</math>, the length of the longer parallel side of each trapezoid.  
 
A square with sides of length <math>1</math> is divided into two congruent trapezoids and a pentagon, which have equal areas, by joining the center of the square with points on three of the sides, as shown. Find <math>x</math>, the length of the longer parallel side of each trapezoid.  
  
−
<center><asy>
+
<center><asy>size(150);
−
pointpen = black; pathpen = black;
+
pointpen = black; pathpen = black+linewidth(0.7);
 
D(unitsquare); D((0,0)); D((1,0)); D((1,1)); D((0,1)); D(D((.5,.5))--D((1,.5))); D(D((.17,1))--(.5,.5)--D((.17,0))); MP("x",(.58,1),N);
 
D(unitsquare); D((0,0)); D((1,0)); D((1,1)); D((0,1)); D(D((.5,.5))--D((1,.5))); D(D((.17,1))--(.5,.5)--D((.17,0))); MP("x",(.58,1),N);
 
</asy></center>
 
</asy></center>
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== Problem 10 ==
 
== Problem 10 ==
−
A large square is divided into a small square surrounded by four congruent rectangles as shown. The perimter of each of the congruent rectangles is <math>14</math>. What is the area of the large square?
+
A large square is divided into a small square surrounded by four congruent rectangles as shown. The perimeter of each of the congruent rectangles is <math>14</math>. What is the area of the large square?
  
−
<center><asy>
+
<center><asy>pathpen = black+linewidth(0.7);
 
D((0,0)--(7,0)--(7,7)--(0,7)--cycle); D((1,0)--(1,6)); D((0,6)--(6,6)); D((1,1)--(7,1)); D((6,7)--(6,1));
 
D((0,0)--(7,0)--(7,7)--(0,7)--cycle); D((1,0)--(1,6)); D((0,6)--(6,6)); D((1,1)--(7,1)); D((6,7)--(6,1));
 
</asy></center>
 
</asy></center>
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== Problem 16 ==
 
== Problem 16 ==
 
The figure shown is the union of a circle and two semicircles of diameters <math>a</math> and <math>b</math>, all of whose centers are collinear. The ratio of the area, of the shaded region to that of the unshaded region is
 
The figure shown is the union of a circle and two semicircles of diameters <math>a</math> and <math>b</math>, all of whose centers are collinear. The ratio of the area, of the shaded region to that of the unshaded region is
 +
 +
[[Image:Problem 16.png|center|###px]]
  
 
<math> \mathrm{(A) \ } \sqrt{\frac ab} \qquad \mathrm{(B) \ }\frac ab \qquad \mathrm{(C) \ } \frac{a^2}{b^2} \qquad \mathrm{(D) \ }\frac{a+b}{2b} \qquad \mathrm{(E) \ } \frac{a^2 + 2ab}{b^2 + 2ab}</math>
 
<math> \mathrm{(A) \ } \sqrt{\frac ab} \qquad \mathrm{(B) \ }\frac ab \qquad \mathrm{(C) \ } \frac{a^2}{b^2} \qquad \mathrm{(D) \ }\frac{a+b}{2b} \qquad \mathrm{(E) \ } \frac{a^2 + 2ab}{b^2 + 2ab}</math>
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What is the value of <math>f(1998)?</math>
 
What is the value of <math>f(1998)?</math>
  
−
<math> \mathrm{(A) \ } \qquad \mathrm{(B) \ } \qquad \mathrm{(C) \ } \qquad \mathrm{(D) \ } \qquad \mathrm{(E) \ } </math>
+
<math>\mathrm{(A)}\ 0
 +
\qquad\mathrm{(B)}\ 2
 +
\qquad\mathrm{(C)}\ 1996
 +
\qquad\mathrm{(D)}\ 1998
 +
\qquad\mathrm{(E)}\ 2000</math>
 +
 
  
 
[[1998 AHSME Problems/Problem 17|Solution]]
 
[[1998 AHSME Problems/Problem 17|Solution]]
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== Problem 24 ==
 
== Problem 24 ==
−
Call a <math>7</math>-digit telephone number <math>d_1d_2d_3-d_4d_5d_6d_7</math> ''memorable'' if the prefix sequence <math>d_1d_2d_3</math> is exactly the same as either of the sequences <math>d_4d_5d_6</math> or <math>d_5d_6d_7</math> (possibly both). Assuming that each <math>d_i</math> can be any of the ten decimal digits <math>0,1,2, \ldots 9</math>, the number of difference memorable telephone numbers is  
+
Call a <math>7</math>-digit telephone number <math>d_1d_2d_3-d_4d_5d_6d_7</math> ''memorable'' if the prefix sequence <math>d_1d_2d_3</math> is exactly the same as either of the sequences <math>d_4d_5d_6</math> or <math>d_5d_6d_7</math> (possibly both). Assuming that each <math>d_i</math> can be any of the ten decimal digits <math>0,1,2, \ldots 9</math>, the number of different memorable telephone numbers is  
  
 
<math> \mathrm{(A) \ } 19,810 \qquad \mathrm{(B) \ } 19,910 \qquad \mathrm{(C) \ } 19,990 \qquad \mathrm{(D) \ } 20,000 \qquad \mathrm{(E) \ } 20,100 </math>
 
<math> \mathrm{(A) \ } 19,810 \qquad \mathrm{(B) \ } 19,910 \qquad \mathrm{(C) \ } 19,990 \qquad \mathrm{(D) \ } 20,000 \qquad \mathrm{(E) \ } 20,100 </math>
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== See also ==
 
== See also ==
−
*[[AHSME]]
+
 
 +
* [[AMC 12 Problems and Solutions]]
 +
* [[Mathematics competition resources]]
 +
 
 +
{{AHSME box|year=1998|before=[[1997 AHSME]]|after=[[1999 AHSME]]}} 
 +
 
 +
{{MAA Notice}}

Latest revision as of 09:40, 11 August 2020

1998 AHSME (Answer Key)
Printable versions: Wiki • AoPS Resources • PDF

Instructions

  1. This is a 30-question, multiple choice test. Each question is followed by answers marked A, B, C, D and E. Only one of these is correct.
  2. You will receive 5 points for each correct answer, 2 points for each problem left unanswered, and 0 points for each incorrect answer.
  3. No aids are permitted other than scratch paper, graph paper, ruler, compass, protractor and erasers.
  4. Figures are not necessarily drawn to scale.
  5. You will have 90 minutes working time to complete the test.
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 • 26 • 27 • 28 • 29 • 30

Problem 1

Each of the sides of five congruent rectangles is labeled with an integer. In rectangle A, $w = 4, x = 1, y = 6, z = 9$. In rectangle B, $w = 1, x = 0, y = 3, z = 6$. In rectangle C, $w = 3, x = 8, y = 5, z = 2$. In rectangle D, $w = 7, x = 5, y = 4, z = 8$. In rectangle E, $w = 9, x = 2, y = 7, z = 0$. These five rectangles are placed, without rotating or reflecting, in position as below. Which of the rectangle is the top leftmost one?

[asy] draw((0,5)--(0,7)--(3,7)--(3,5)--cycle); draw((0,4)--(9,4)--(9,2)--(6,2)--(6,0)--(0,0)--cycle); draw((3,0)--(3,4));draw((6,2)--(6,4));draw((0,2)--(6,2)); label("$w$",(0,6),(-1,0));label("$x$",(1.5,7),(0,1));label("$y$",(3,6),(1,0));label("$z$",(1.5,5),(0,-1)); [/asy]

$\mathrm{(A)\ } A \qquad \mathrm{(B) \ }B \qquad \mathrm{(C) \ } C \qquad \mathrm{(D) \ } D \qquad \mathrm{(E) \ }E$

Solution

Problem 2

Letters $A,B,C,$ and $D$ represent four different digits selected from $0,1,2,\ldots ,9.$ If $(A+B)/(C+D)$ is an integer that is as large as possible, what is the value of $A+B$?

$\mathrm{(A) \ }13 \qquad \mathrm{(B) \ }14 \qquad \mathrm{(C) \ } 15\qquad \mathrm{(D) \ }16 \qquad \mathrm{(E) \ } 17$

Solution

Problem 3

If $\texttt{a,b,}$ and $\texttt{c}$ are digits for which

\[\begin{array}{rccc}&\ \texttt{7}& \texttt{a}&\texttt{2}\\ -&\ \texttt{4}&\texttt{8}&\texttt{b} \\ \hline &\ \texttt{c}&\texttt{7}& \texttt{3} \end{array}\]

then $\texttt{a+b+c =}$

$\mathrm{(A) \ }14 \qquad \mathrm{(B) \ }15 \qquad \mathrm{(C) \ }16 \qquad \mathrm{(D) \ }17 \qquad \mathrm{(E) \ }18$

Solution

Problem 4

Define $[a,b,c]$ to mean $\frac {a+b}c$, where $c \neq 0$. What is the value of

$\left[[60,30,90],[2,1,3],[10,5,15]\right]?$

$\mathrm{(A) \ }0 \qquad \mathrm{(B) \ }0.5 \qquad \mathrm{(C) \ }1 \qquad \mathrm{(D) \ }1.5 \qquad \mathrm{(E) \ }2$

Solution

Problem 5

If $2^{1998}-2^{1997}-2^{1996}+2^{1995} = k \cdot 2^{1995},$ what is the value of $k$?

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

Solution

Problem 6

If $1998$ is written as a product of two positive integers whose difference is as small as possible, then the difference is

$\mathrm{(A) \ }8 \qquad \mathrm{(B) \ }15 \qquad \mathrm{(C) \ }17 \qquad \mathrm{(D) \ }47 \qquad \mathrm{(E) \ } 93$

Solution

Problem 7

If $N > 1$, then $\sqrt[3]{N\sqrt[3]{N\sqrt[3]{N}}} =$

$\mathrm{(A) \ } N^{\frac 1{27}} \qquad \mathrm{(B) \ } N^{\frac 1{9}} \qquad \mathrm{(C) \ } N^{\frac 1{3}} \qquad \mathrm{(D) \ } N^{\frac {13}{27}} \qquad \mathrm{(E) \ } N$

Solution

Problem 8

A square with sides of length $1$ is divided into two congruent trapezoids and a pentagon, which have equal areas, by joining the center of the square with points on three of the sides, as shown. Find $x$, the length of the longer parallel side of each trapezoid.

[asy]size(150); pointpen = black; pathpen = black+linewidth(0.7); D(unitsquare); D((0,0)); D((1,0)); D((1,1)); D((0,1)); D(D((.5,.5))--D((1,.5))); D(D((.17,1))--(.5,.5)--D((.17,0))); MP("x",(.58,1),N); [/asy]

$\mathrm{(A) \ } \frac 35 \qquad \mathrm{(B) \ } \frac 23 \qquad \mathrm{(C) \ } \frac 34 \qquad \mathrm{(D) \ } \frac 56 \qquad \mathrm{(E) \ } \frac 78$

Solution

Problem 9

A speaker talked for sixty minutes to a full auditorium. Twenty percent of the audience heard the entire talk and ten percent slept through the entire talk. Half of the remainder heard one third of the talk and the other half heard two thirds of the talk. What was the average number of minutes of the talk heard by members of the audience?

$\mathrm{(A) \ } 24 \qquad \mathrm{(B) \ } 27\qquad \mathrm{(C) \ }30 \qquad \mathrm{(D) \ }33 \qquad \mathrm{(E) \ }36$

Solution

Problem 10

A large square is divided into a small square surrounded by four congruent rectangles as shown. The perimeter of each of the congruent rectangles is $14$. What is the area of the large square?

[asy]pathpen = black+linewidth(0.7); D((0,0)--(7,0)--(7,7)--(0,7)--cycle); D((1,0)--(1,6)); D((0,6)--(6,6)); D((1,1)--(7,1)); D((6,7)--(6,1)); [/asy]

$\mathrm{(A) \ }49 \qquad \mathrm{(B) \ }64 \qquad \mathrm{(C) \ }100 \qquad \mathrm{(D) \ }121 \qquad \mathrm{(E) \ }196$

Solution

Problem 11

Let $R$ be a rectangle. How many circles in the plane of $R$ have a diameter both of whose endpoints are vertices of $R$?

$\mathrm{(A) \ }1 \qquad \mathrm{(B) \ }2 \qquad \mathrm{(C) \ }4 \qquad \mathrm{(D) \ }5 \qquad \mathrm{(E) \ }6$

Solution

Problem 12

How many different prime numbers are factors of $N$ if

$\log_2 ( \log_3 ( \log_5 (\log_ 7 N))) = 11?$

$\mathrm{(A) \ }1 \qquad \mathrm{(B) \ }2 \qquad \mathrm{(C) \ }3 \qquad \mathrm{(D) \ } 4\qquad \mathrm{(E) \ }7$

Solution

Problem 13

Walter rolls four standard six-sided dice and finds that the product of the numbers of the upper faces is $144$. Which of he following could not be the sum of the upper four faces?

$\mathrm{(A) \ }14 \qquad \mathrm{(B) \ }15 \qquad \mathrm{(C) \ }16 \qquad \mathrm{(D) \ }17 \qquad \mathrm{(E) \ }18$

Solution

Problem 14

A parabola has vertex of $(4,-5)$ and has two $x-$intercepts, one positive, and one negative. If this parabola is the graph of $y = ax^2 + bx + c,$ which of $a,b,$ and $c$ must be positive?

$\mathrm{(A) \ } \text{only}\ a \qquad \mathrm{(B) \ } \text{only}\ b \qquad \mathrm{(C) \ } \text{only}\ c \qquad \mathrm{(D) \ } a\ \text{and}\ b\ \text{only} \qquad \mathrm{(E) \ } \text{none}$

Solution

Problem 15

A regular hexagon and an equilateral triangle have equal areas. What is the ratio of the length of a side of the triangle to the length of a side of the hexagon?

$\mathrm{(A) \ }\sqrt{3} \qquad \mathrm{(B) \ }2 \qquad \mathrm{(C) \ }\sqrt{6} \qquad \mathrm{(D) \ }3 \qquad \mathrm{(E) \ }6$

Solution

Problem 16

The figure shown is the union of a circle and two semicircles of diameters $a$ and $b$, all of whose centers are collinear. The ratio of the area, of the shaded region to that of the unshaded region is

###px

$\mathrm{(A) \ } \sqrt{\frac ab} \qquad \mathrm{(B) \ }\frac ab \qquad \mathrm{(C) \ } \frac{a^2}{b^2} \qquad \mathrm{(D) \ }\frac{a+b}{2b} \qquad \mathrm{(E) \ } \frac{a^2 + 2ab}{b^2 + 2ab}$

Solution

Problem 17

Let $f(x)$ be a function with the two properties:

(a) for any two real numbers $x$ and $y$, $f(x+y) = x + f(y)$, and
(b) $f(0) = 2.$

What is the value of $f(1998)?$

$\mathrm{(A)}\ 0 \qquad\mathrm{(B)}\ 2 \qquad\mathrm{(C)}\ 1996 \qquad\mathrm{(D)}\ 1998 \qquad\mathrm{(E)}\ 2000$


Solution

Problem 18

A right circular cone of volume $A$, a right circular cylinder of volume $M$, and a sphere of volume $C$ all have the same radius, and the common height of the cone and the cylinder is equal to the diameter of the sphere. Then

$\mathrm{(A) \ } A-M+C = 0 \qquad \mathrm{(B) \ } A+M=C \qquad \mathrm{(C) \ } 2A = M+C \qquad \mathrm{(D) \ }A^2 - M^2 + C^2 = 0 \qquad \mathrm{(E) \ } 2A + 2M = 3C$

Solution

Problem 19

How many triangles have area $10$ and vertices at $(-5,0),(5,0)$ and $(5\cos \theta, 5\sin \theta)$ for some angle $\theta$?

$\mathrm{(A) \ }0 \qquad \mathrm{(B) \ }2 \qquad \mathrm{(C) \ }4 \qquad \mathrm{(D) \ }6 \qquad \mathrm{(E) \ } 8$

Solution

Problem 20

Three cards, each with a positive integer written on it, are lying face-down on a table. Casey, Stacy, and Tracy are told that

(a) the numbers are all different,
(b) they sum to $13$, and
(c) they are in increasing order, left to right.

First, Casey looks at the number on the leftmost card and says, "I don't have enough information to determine the other two numbers." Then Tracy looks at the number on the rightmost card and says, "I don't have enough information to determine the other two numbers." Finally, Stacy looks at the number on the middle card and says, "I don't have enough information to determine the other two numbers." Assume that each person knows that the other two reason perfectly and hears their comments. What number is on the middle card?

$\textrm{(A)}\ 2 \qquad \textrm{(B)}\ 3 \qquad \textrm{(C)}\ 4 \qquad \textrm{(D)}\ 5 \qquad \textrm{(E)}\ \text{There is not enough information to determine the number.}$

Solution

Problem 21

In an $h$-meter race, Sunny is exactly $d$ meters ahead of Windy when Sunny finishes the race. The next time they race, Sunny sportingly starts $d$ meters behind Windy, who is at the starting line. Both runners run at the same constant speed as they did in the first race. How many meters ahead is Sunny when Sunny finishes the second race?

$\mathrm{(A) \ } \frac dh \qquad \mathrm{(B) \ } 0 \qquad \mathrm{(C) \ } \frac {d^2}h \qquad \mathrm{(D) \ } \frac {h^2}d \qquad \mathrm{(E) \ } \frac{d^2}{h-d}$

Solution

Problem 22

What is the value of the expression

$\frac {1}{\log_{2}100!} + \frac {1}{\log_{3}100!} + \frac {1}{\log_{4}100!} + \cdots + \frac {1}{\log_{100}100!}$

$\mathrm{(A) \ }0.01 \qquad \mathrm{(B) \ }0.1 \qquad \mathrm{(C) \ }1 \qquad \mathrm{(D) \ }2 \qquad \mathrm{(E) \ } 10$

Solution

Problem 23

The graphs of $x^2 + y^2 = 4 + 12x + 6y$ and $x^2 + y^2 = k + 4x + 12y$ intersect when $k$ satisfies $a \le k \le b$, and for no other values of $k$. Find $b-a$.

$\mathrm{(A) \ }5 \qquad \mathrm{(B) \ }68 \qquad \mathrm{(C) \ }104 \qquad \mathrm{(D) \ }140 \qquad \mathrm{(E) \ }144$

Solution

Problem 24

Call a $7$-digit telephone number $d_1d_2d_3-d_4d_5d_6d_7$ memorable if the prefix sequence $d_1d_2d_3$ is exactly the same as either of the sequences $d_4d_5d_6$ or $d_5d_6d_7$ (possibly both). Assuming that each $d_i$ can be any of the ten decimal digits $0,1,2, \ldots 9$, the number of different memorable telephone numbers is

$\mathrm{(A) \ } 19,810 \qquad \mathrm{(B) \ } 19,910 \qquad \mathrm{(C) \ } 19,990 \qquad \mathrm{(D) \ } 20,000 \qquad \mathrm{(E) \ } 20,100$

Solution

Problem 25

A piece of graph paper is folded once so that $(0,2)$ is matched with $(4,0)$, and $(7,3)$ is matched with $(m,n)$. Find $m+n$.

$\mathrm{(A) \ }6.7 \qquad \mathrm{(B) \ }6.8 \qquad \mathrm{(C) \ }6.9 \qquad \mathrm{(D) \ }7.0 \qquad \mathrm{(E) \ }8.0$

Solution

Problem 26

In quadrilateral $ABCD$, it is given that $\angle A = 120^{\circ}$, angles $B$ and $D$ are right angles, $AB = 13$, and $AD = 46$. Then $AC=$

$\mathrm{(A) \ } 60 \qquad \mathrm{(B) \ }62 \qquad \mathrm{(C) \ }64 \qquad \mathrm{(D) \ }65 \qquad \mathrm{(E) \ } 72$

Solution

Problem 27

A $9 \times 9 \times 9$ cube is composed of twenty-seven $3 \times 3 \times 3$ cubes. The big cube is ‘tunneled’ as follows: First the six $3 \times 3 \times 3$ cubes which make up the center of each face as well as the center $3 \times 3 \times 3$ cube are removed as shown. Second, each of the twenty remaining $3 \times 3 \times 3$ cubes is diminished in the same way. That is, the center facial unit cubes as well as each center cube are removed. The surface area of the final figure is

1998 AHSME num. 27.png

$\mathrm{(A) \ } 384 \qquad \mathrm{(B) \ } 729 \qquad \mathrm{(C) \ } 864 \qquad \mathrm{(D) \ } 1024 \qquad \mathrm{(E) \ } 1056$

Solution

Problem 28

In triangle $ABC$, angle $C$ is a right angle and $CB > CA$. Point $D$ is located on $\overline{BC}$ so that angle $CAD$ is twice angle $DAB$. If $AC/AD = 2/3$, then $CD/BD = m/n$, where $m$ and $n$ are relatively prime positive integers. Find $m+n$.

$\mathrm{(A) \ }10 \qquad \mathrm{(B) \ }14 \qquad \mathrm{(C) \ }18 \qquad \mathrm{(D) \ }22 \qquad \mathrm{(E) \ } 26$

Solution

Problem 29

A point $(x,y)$ in the plane is called a lattice point if both $x$ and $y$ are integers. The area of the largest square that contains exactly three lattice points in its interior is closest to

$\mathrm{(A) \ } 4.0 \qquad \mathrm{(B) \ } 4.2 \qquad \mathrm{(C) \ } 4.5 \qquad \mathrm{(D) \ } 5.0 \qquad \mathrm{(E) \ } 5.6$

Solution

Problem 30

For each positive integer $n$, let

$a_n = \frac{(n+9)!}{(n-1)!}$

Let $k$ denote the smallest positive integer for which the rightmost nonzero digit of $a_k$ is odd. The rightmost nonzero digit of $a_k$ is

$\mathrm{(A) \ }1 \qquad \mathrm{(B) \ }3 \qquad \mathrm{(C) \ }5 \qquad \mathrm{(D) \ } 7 \qquad \mathrm{(E) \ } 9$

Solution


See also

1998 AHSME (Problems • Answer Key • Resources)
Preceded by
1997 AHSME 		Followed by
1999 AHSME
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 • 26 • 27 • 28 • 29 • 30
All AHSME Problems and Solutions


The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. AMC logo.png

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