Difference between revisions of "1991 AHSME Problems"

Latest revision as of 03:27, 6 September 2021

1991 AHSME (Answer Key) Printable versions: Wiki • AoPS Resources • PDF
Instructions 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. You will receive 5 points for each correct answer, 2 points for each problem left unanswered, and 0 points for each incorrect answer. No aids are permitted other than scratch paper, graph paper, ruler, compass, protractor and erasers. Figures are not necessarily drawn to scale. You will have 90 minutes working time to complete the test.
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Problem 1

If for any three distinct numbers $a$ , $b$ , and $c$ we define $f(a,b,c)=\frac{c+a}{c-b}$ , then $f(1,-2,-3)$ is

$\textbf{(A) } -2 \qquad \textbf{(B) } -\frac{2}{5} \qquad \textbf{(C) } -\frac{1}{4} \qquad \textbf{(D) } \frac{2}{5} \qquad \textbf {(E) } 2$

Solution

Problem 2

$|3-\pi|=$

$\textbf{(A) }\frac{1}{7} \qquad \textbf{(B) }0.14 \qquad \textbf{(C) }3-\pi \qquad \textbf{(D) }3+\pi \qquad \textbf{(E) }\pi-3$

Solution

Problem 3

$(4^{-1}-3^{-1})^{-1}=$

$\textbf{(A) }-12 \qquad \textbf{(B) }-1 \qquad \textbf{(C) }\frac{1}{12} \qquad \textbf{(D) }1 \qquad \textbf{(E) }12$

Solution

Problem 4

Which of the following triangles cannot exist?

$\textbf{(A) }$ An acute isosceles triangle

$\textbf{(B) }$ An isosceles right triangle

$\textbf{(C) }$ An obtuse right triangle

$\textbf{(D) }$ A scalene right triangle

$\textbf{(E) }$ A scalene obtuse triangle

Solution

Problem 5

$[asy] draw((0,0)--(2,2)--(2,1)--(5,1)--(5,-1)--(2,-1)--(2,-2)--cycle,dot); MP("A",(0,0),W);MP("B",(2,2),N);MP("C",(2,1),S);MP("D",(5,1),NE);MP("E",(5,-1),SE);MP("F",(2,-1),NW);MP("G",(2,-2),S); MP("5",(2,1.5),E);MP("5",(2,-1.5),E);MP("20",(3.5,1),N);MP("20",(3.5,-1),S);MP("10",(5,0),E); [/asy]$

In the arrow-shaped polygon [see figure], the angles at vertices $A,C,D,E$ and $F$ are right angles, $BC=FG=5, CD=FE=20, DE=10$ , and $AB=AG$ . The area of the polygon is closest to

$\textbf{(A) } 288\qquad\textbf{(B) } 291\qquad\textbf{(C) } 294\qquad\textbf{(D) } 297\qquad\textbf{(E) } 300$

Solution

Problem 6

If $x\geq 0$ , then $\sqrt{x\sqrt{x\sqrt{x}}}=$

$\textbf{(A) } x\sqrt{x}\qquad \textbf{(B) } x\sqrt[4]{x}\qquad \textbf{(C) } \sqrt[8]{x}\qquad \textbf{(D) } \sqrt[8]{x^3}\qquad \textbf{(E) } \sqrt[8]{x^7}$

Solution

Problem 7

If $x=\frac{a}{b}$ , $a\neq b$ and $b\neq 0$ , then $\frac{a+b}{a-b}=$

$\textbf{(A) } \frac{x}{x+1} \qquad \textbf{(B) } \frac{x+1}{x-1} \qquad \textbf{(C) } 1 \qquad \textbf{(D) } x-\frac{1}{x} \qquad \textbf{(E) } x+\frac{1}{x}$

Solution

Problem 8

Liquid $X$ does not mix with water. Unless obstructed, it spreads out on the surface of water to form a circular film $0.1$ cm thick. A rectangular box measuring $6$ cm by $3$ cm by $12$ cm is filled with liquid $X$ . Its contents are poured onto a large body of water. What will be the radius, in centimeters, of the resulting circular film?

$\textbf{(A) } \frac{\sqrt{216}}{\pi} \qquad \textbf{(B) }\sqrt{\frac{216}{\pi}} \qquad \textbf{(C) } \sqrt{\frac{2160}{\pi}} \qquad \textbf{(D) } \frac{216}{\pi} \qquad \textbf{(E) } \frac{2160}{\pi}$

Solution

Problem 9

From time $t=0$ to time $t=1$ a population increased by $i\%$ , and from time $t=1$ to time $t=2$ the population increased by $j\%$ . Therefore, from time $t=0$ to time $t=2$ the population increased by

$\textbf{(A) } (i+j)\% \qquad \textbf{(B) } ij\% \qquad \textbf{(C) } (i+ij)\% \qquad \textbf{(D) } \left(i+j+\frac{ij}{100}\right)\% \qquad \textbf{(E) } \left(i+j+\frac{i+j}{100}\right)\%$

Solution

Problem 10

Point $P$ is $9$ units from the center of a circle of radius $15$ . How many different chords of the circle contain $P$ and have integer lengths?

$\textbf{(A) } 11\qquad \textbf{(B) } 12\qquad \textbf{(C) } 13\qquad \textbf{(D) } 14\qquad \textbf{(E) } 29$

Solution

Problem 11

Jack and Jill run 10 km. They start at the same point, run 5 km up a hill, and return to the starting point by the same route. Jack has a 10 minute head start and runs at the rate of 15 km/hr uphill and 20 km/hr downhill. Jill runs 16 km/hr uphill and 22 km/hr downhill. How far from the top of the hill are they when they pass each other going in opposite directions (in km)?

$\textbf{(A) } \frac{5}{4}\qquad \textbf{(B) } \frac{35}{27}\qquad \textbf{(C) } \frac{27}{20}\qquad \textbf{(D) } \frac{7}{3}\qquad \textbf{(E) } \frac{28}{49}$

Solution

Problem 12

The measures (in degrees) of the interior angles of a convex hexagon form an arithmetic sequence of integers. Let $m$ be the measure of the largest interior angle of the hexagon. The largest possible value of $m$ , in degrees, is

$\textbf{(A) } 165\qquad \textbf{(B) } 167\qquad \textbf{(C) } 170\qquad \textbf{(D) } 175\qquad \textbf{(E) } 179$

Solution

Problem 13

Horses $X,Y$ and $Z$ are entered in a three-horse race in which ties are not possible. The odds against $X$ winning are $3:1$ and the odds against $Y$ winning are $2:3$ , what are the odds against $Z$ winning? (By "odds against $H$ winning are $p:q$ " we mean the probability of $H$ winning the race is $\frac{q}{p+q}$ .)

$\textbf{(A) } 3:20\qquad \textbf{(B) } 5:6\qquad \textbf{(C) } 8:5\qquad \textbf{(D) } 17:3\qquad \textbf{(E) } 20:3$

Solution

Problem 14

If $x$ is the cube of a positive integer and $d$ is the number of positive integers that are divisors of $x$ , then $d$ could be

$\textbf{(A) } 200\qquad \textbf{(B) } 201\qquad \textbf{(C) } 202\qquad \textbf{(D) } 203\qquad \textbf{(E) } 204$

Solution

Problem 15

A circular table has 60 chairs around it. There are $N$ people seated at this table in such a way that the next person seated must sit next to someone. What is the smallest possible value for $N$ ?

$\textbf{(A) } 15\qquad \textbf{(B) } 20\qquad \textbf{(C) } 30\qquad \textbf{(D) } 40\qquad \textbf{(E) } 58$

Solution

Problem 16

One hundred students at Century High School participated in the AHSME last year, and their mean score was 100. The number of non-seniors taking the AHSME was $50\%$ more than the number of seniors, and the mean score of the seniors was $50\%$ higher than that of the non-seniors. What was the mean score of the seniors?

$\textbf{(A) } 100\qquad \textbf{(B) } 112.5\qquad \textbf{(C) } 120\qquad \textbf{(D) } 125\qquad \textbf{(E) } 150$

Solution

Problem 17

A positive integer $N$ is a palindrome if the integer obtained by reversing the sequence of digits of $N$ is equal to $N$ . The year 1991 is the only year in the current century with the following 2 properties:

(a) It is a palindrome (b) It factors as a product of a 2-digit prime palindrome and a 3-digit prime palindrome.

How many years in the millenium between 1000 and 2000 have properties (a) and (b)?

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

Solution

Problem 18

If $S$ is the set of points $z$ in the complex plane such that $(3+4i)z$ is a real number, then $S$ is a

$\textbf{(A) }$ right triangle $\qquad \textbf{(B) }$ circle $\qquad \textbf{(C) }$ hyperbola $\qquad \textbf{(D) }$ line $\qquad \textbf{(E) }$ parabola

Solution

Problem 19

$[asy] draw((0,0)--(0,3)--(4,0)--cycle,dot); draw((4,0)--(7,0)--(7,10)--cycle,dot); draw((0,3)--(7,10),dot); MP("C",(0,0),SW);MP("A",(0,3),NW);MP("B",(4,0),S);MP("E",(7,0),SE);MP("D",(7,10),NE); [/asy]$

Triangle $ABC$ has a right angle at $C, AC=3$ and $BC=4$ . Triangle $ABD$ has a right angle at $A$ and $AD=12$ . Points $C$ and $D$ are on opposite sides of $\overline{AB}$ . The line through $D$ parallel to $\overline{AC}$ meets $\overline{CB}$ extended at $E$ . If $\frac{DE}{DB}=\frac{m}{n},$ where $m$ and $n$ are relatively prime positive integers, then $m+n$ is

$\textbf{(A) } 25\qquad \textbf{(B) } 128\qquad \textbf{(C) } 153\qquad \textbf{(D) } 243\qquad \textbf{(E) } 256$

Solution

Problem 20

The sum of all real $x$ such that $(2^x-4)^3+(4^x-2)^3=(4^x+2^x-6)^3$ is

$\textbf{(A) } \frac32 \qquad \textbf{(B) } 2 \qquad \textbf{(C) } \frac52 \qquad \textbf{(D) } 3 \qquad \textbf{(E) } \frac72$

Solution

Problem 21

For all real numbers $x$ except $x=0$ and $x=1$ the function $f(x)$ is defined by $f(x/(x-1))=1/x$ . Suppose $0\leq t\leq \pi/2$ . What is the value of $f(\sec^2t)$ ?

$\textbf{(A) } \sin^2\theta\qquad \textbf{(B) } \cos^2\theta\qquad \textbf{(C) } \tan^2\theta\qquad \textbf{(D) } \cot^2\theta\qquad \textbf{(E) } \csc^2\theta$

Solution

Problem 22

$[asy] draw(circle((0,6sqrt(2)),2sqrt(2)),black+linewidth(.75)); draw(circle((0,3sqrt(2)),sqrt(2)),black+linewidth(.75)); draw((-8/3,16sqrt(2)/3)--(-4/3,8sqrt(2)/3)--(0,0)--(4/3,8sqrt(2)/3)--(8/3,16sqrt(2)/3),dot); MP("B",(-8/3,16*sqrt(2)/3),W);MP("B'",(8/3,16*sqrt(2)/3),E); MP("A",(-4/3,8*sqrt(2)/3),W);MP("A'",(4/3,8*sqrt(2)/3),E); MP("P",(0,0),S); [/asy]$

Two circles are externally tangent. Lines $\overline{PAB}$ and $\overline{PA'B'}$ are common tangents with $A$ and $A'$ on the smaller circle $B$ and $B'$ on the larger circle. If $PA=AB=4$ , then the area of the smaller circle is

$\textbf{(A) } 1.44\pi\qquad \textbf{(B) } 2\pi\qquad \textbf{(C) } 2.56\pi\qquad \textbf{(D) } \sqrt{8}\pi\qquad \textbf{(E) } 4\pi$

Solution

Problem 23

$[asy] draw((0,0)--(0,2)--(2,2)--(2,0)--cycle,dot); draw((2,2)--(0,0)--(0,1)--cycle,dot); draw((0,2)--(1,0),dot); MP("B",(0,0),SW);MP("A",(0,2),NW);MP("D",(2,2),NE);MP("C",(2,0),SE); MP("E",(0,1),W);MP("F",(1,0),S);MP("H",(2/3,2/3),E);MP("I",(2/5,6/5),N); dot((1,0));dot((0,1));dot((2/3,2/3));dot((2/5,6/5)); [/asy]$

If $ABCD$ is a $2\times2$ square, $E$ is the midpoint of $\overline{AB}$ , $F$ is the midpoint of $\overline{BC}$ , $\overline{AF}$ and $\overline{DE}$ intersect at $I$ , and $\overline{BD}$ and $\overline{AF}$ intersect at $H$ , then the area of quadrilateral $BEIH$ is

$\textbf{(A) } \frac{1}{3}\qquad \textbf{(B) } \frac{2}{5}\qquad \textbf{(C) } \frac{7}{15}\qquad \textbf{(D) } \frac{8}{15}\qquad \textbf{(E) } \frac{3}{5}$

Solution

Problem 24

The graph, $G$ of $y=\log_{10}x$ is rotated $90^{\circ}$ counter-clockwise about the origin to obtain a new graph $G'$ . Which of the following is an equation for $G'$ ?

$\textbf{(A) } y=\log_{10}\left(\frac{x+90}{9}\right) \qquad \textbf{(B) } y=\log_{x}10 \qquad \textbf{(C) } y=\frac{1}{x+1} \qquad \textbf{(D) } y=10^{-x} \qquad \textbf{(E) } y=10^x$

Solution

Problem 25

If $T_n=1+2+3+\cdots +n$ and $P_n=\frac{T_2}{T_2-1}\cdot\frac{T_3}{T_3-1}\cdot\frac{T_4}{T_4-1}\cdot\cdots\cdot\frac{T_n}{T_n-1}$ for $n=2,3,4,\cdots,$ then $P_{1991}$ is closest to which of the following numbers?

$\textbf{(A) } 2.0\qquad \textbf{(B) } 2.3\qquad \textbf{(C) } 2.6\qquad \textbf{(D) } 2.9\qquad \textbf{(E) } 3.2$

Solution

Problem 26

An $n$ -digit positive integer is cute if its $n$ digits are an arrangement of the set $\{1,2,...,n\}$ and its first $k$ digits form an integer that is divisible by $k$ , for $k = 1,2,...,n$ . For example, $321$ is a cute $3$ -digit integer because $1$ divides $3$ , $2$ divides $32$ , and $3$ divides $321$ . How many cute $6$ -digit integers are there?

$\textbf{(A) } 0\qquad \textbf{(B) } 1\qquad \textbf{(C) } 2\qquad \textbf{(D) } 3\qquad \textbf{(E) } 4$

Solution

Problem 27

If $x+\sqrt{x^2-1}+\frac{1}{x-\sqrt{x^2-1}}=20,$ then $x^2+\sqrt{x^4-1}+\frac{1}{x^2+\sqrt{x^4-1}}=$

$\textbf{(A) } 5.05 \qquad \textbf{(B) } 20 \qquad \textbf{(C) } 51.005 \qquad \textbf{(D) } 61.25 \qquad \textbf{(E) } 400$

Solution

Problem 28

Initially an urn contains 100 white and 100 black marbles. Repeatedly 3 marbles are removed (at random) from the urn and replaced with some marbles from a pile outside the urn as follows: 3 blacks are replaced with 1 black, or 2 blacks and 1 white are replaced with a white and a black, or 1 black and 2 whites are replaced with 2 whites, or 3 whites are replaced with a black and a white. Which of the following could be the contents of the urn after repeated applications of this procedure?

$\textbf{(A) }$ 2 black $\qquad \textbf{(B) }$ 2 white $\qquad \textbf{(C) }$ 1 black $\qquad \textbf{(D) }$ 1 black and 1 white $\qquad \textbf{(E) }$ 1 white

Solution

Problem 29

Equilateral triangle $ABC$ has $P$ on $AB$ and $Q$ on $AC$ . The triangle is folded along $PQ$ so that vertex $A$ now rests at $A'$ on side $BC$ . If $BA'=1$ and $A'C=2$ then the length of the crease $PQ$ is

$\textbf{(A) } \frac{8}{5} \qquad \textbf{(B) } \frac{7}{20}\sqrt{21} \qquad \textbf{(C) } \frac{1+\sqrt{5}}{2} \qquad \textbf{(D) } \frac{13}{8} \qquad \textbf{(E) } \sqrt{3}$

Solution

Problem 30

For any set $S$ , let $|S|$ denote the number of elements in $S$ , and let $n(S)$ be the number of subsets of $S$ , including the empty set and the set $S$ itself. If $A$ , $B$ , and $C$ are sets for which $n(A)+n(B)+n(C)=n(A\cup B\cup C)$ and $|A|=|B|=100$ , then what is the minimum possible value of $|A\cap B\cap C|$ ?

$\textbf{(A) } 96 \qquad \textbf{(B) } 97 \qquad \textbf{(C) } 98 \qquad \textbf{(D) } 99 \qquad \textbf{(E) } 100$

Solution

1991 AHSME (Problems • Answer Key • Resources)
Preceded by 1990 AHSME	Followed by 1992 AHSME
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Difference between revisions of "1991 AHSME Problems"

Latest revision as of 03:27, 6 September 2021

Contents

Problem 1

Problem 2

Problem 3

Problem 4

Problem 5

Problem 6

Problem 7

Problem 8

Problem 9

Problem 10

Problem 11

Problem 12

Problem 13

Problem 14

Problem 15

Problem 16

Problem 17

Problem 18

Problem 19

Problem 20

Problem 21

Problem 22

Problem 23

Problem 24

Problem 25

Problem 26

Problem 27

Problem 28

Problem 29

Problem 30

See also

@@ Line 1: / Line 1: @@
-Link to full test below.
+{{AHSME Problems|year = 1991}}
-http://www.artofproblemsolving.com/Forum/resources.php?c=182&cid=44&year=1991&sid=23c56fcb006bee49b72650509fbedb9b
+== Problem 1 ==
+If for any three distinct numbers <math>a</math>, <math>b</math>, and <math>c</math> we define <math>f(a,b,c)=\frac{c+a}{c-b}</math>, then <math>f(1,-2,-3)</math> is
+<math> \textbf{(A) } -2 \qquad \textbf{(B) } -\frac{2}{5} \qquad \textbf{(C) } -\frac{1}{4} \qquad \textbf{(D) } \frac{2}{5} \qquad \textbf {(E) } 2 </math>
+[[1991 AHSME Problems/Problem 1|Solution]]
+== Problem 2 ==
+<math>|3-\pi|=</math>
+<math> \textbf{(A) }\frac{1}{7} \qquad \textbf{(B) }0.14 \qquad \textbf{(C) }3-\pi \qquad \textbf{(D) }3+\pi \qquad \textbf{(E) }\pi-3 </math>
+[[1991 AHSME Problems/Problem 2|Solution]]
+== Problem 3 ==
+<math>(4^{-1}-3^{-1})^{-1}=</math>
+<math> \textbf{(A) }-12 \qquad \textbf{(B) }-1 \qquad \textbf{(C) }\frac{1}{12} \qquad \textbf{(D) }1 \qquad \textbf{(E) }12 </math>
+[[1991 AHSME Problems/Problem 3|Solution]]
+== Problem 4 ==
+Which of the following triangles cannot exist?
+<math>\textbf{(A) }</math> An acute isosceles triangle
+<math>\textbf{(B) }</math> An isosceles right triangle
+<math>\textbf{(C) }</math> An obtuse right triangle
+<math>\textbf{(D) }</math> A scalene right triangle
+<math>\textbf{(E) }</math> A scalene obtuse triangle
+[[1991 AHSME Problems/Problem 4|Solution]]
+== Problem 5 ==
+<asy>
+draw((0,0)--(2,2)--(2,1)--(5,1)--(5,-1)--(2,-1)--(2,-2)--cycle,dot);
+MP("A",(0,0),W);MP("B",(2,2),N);MP("C",(2,1),S);MP("D",(5,1),NE);MP("E",(5,-1),SE);MP("F",(2,-1),NW);MP("G",(2,-2),S);
+MP("5",(2,1.5),E);MP("5",(2,-1.5),E);MP("20",(3.5,1),N);MP("20",(3.5,-1),S);MP("10",(5,0),E);
+</asy>
+In the arrow-shaped polygon [see figure], the angles at vertices <math>A,C,D,E</math> and <math>F</math> are right angles, <math>BC=FG=5, CD=FE=20, DE=10</math>, and <math>AB=AG</math>. The area of the polygon is closest to
+<math>\textbf{(A) } 288\qquad\textbf{(B) } 291\qquad\textbf{(C) } 294\qquad\textbf{(D) } 297\qquad\textbf{(E) } 300</math>
+[[1991 AHSME Problems/Problem 5|Solution]]
+== Problem 6 ==
+If <math>x\geq 0</math>, then <math>\sqrt{x\sqrt{x\sqrt{x}}}=</math>
+<math>\textbf{(A) } x\sqrt{x}\qquad
+\textbf{(B) } x\sqrt[4]{x}\qquad
+\textbf{(C) } \sqrt[8]{x}\qquad
+\textbf{(D) } \sqrt[8]{x^3}\qquad
+\textbf{(E) } \sqrt[8]{x^7}</math>
+[[1991 AHSME Problems/Problem 6|Solution]]
+== Problem 7 ==
+If <math>x=\frac{a}{b}</math>, <math>a\neq b</math> and <math>b\neq 0</math>, then <math>\frac{a+b}{a-b}=</math>
+<math>\textbf{(A) } \frac{x}{x+1} \qquad \textbf{(B) } \frac{x+1}{x-1} \qquad \textbf{(C) } 1 \qquad \textbf{(D) } x-\frac{1}{x} \qquad \textbf{(E) } x+\frac{1}{x}</math>
+[[1991 AHSME Problems/Problem 7|Solution]]
+== Problem 8 ==
+Liquid <math>X</math> does not mix with water. Unless obstructed, it spreads out on the surface of water to form a circular film <math>0.1</math>cm thick. A rectangular box measuring <math>6</math>cm by <math>3</math>cm by <math>12</math>cm is filled with liquid <math>X</math>. Its contents are poured onto a large body of water. What will be the radius, in centimeters, of the resulting circular film?
+<math>\textbf{(A) } \frac{\sqrt{216}}{\pi} \qquad \textbf{(B) }\sqrt{\frac{216}{\pi}} \qquad \textbf{(C) } \sqrt{\frac{2160}{\pi}} \qquad \textbf{(D) } \frac{216}{\pi} \qquad \textbf{(E) } \frac{2160}{\pi}</math>
+[[1991 AHSME Problems/Problem 8|Solution]]
+== Problem 9 ==
+From time <math>t=0</math> to time <math>t=1</math> a population increased by <math>i\%</math>, and from time <math>t=1</math> to time <math>t=2</math> the population increased by <math>j\%</math>. Therefore, from time <math>t=0</math> to time <math>t=2</math> the population increased by
+<math>\textbf{(A) } (i+j)\% \qquad
+\textbf{(B) } ij\% \qquad
+\textbf{(C) } (i+ij)\% \qquad
+\textbf{(D) } \left(i+j+\frac{ij}{100}\right)\% \qquad
+\textbf{(E) } \left(i+j+\frac{i+j}{100}\right)\%</math>
+[[1991 AHSME Problems/Problem 9|Solution]]
+== Problem 10 ==
+Point <math>P</math> is <math>9</math> units from the center of a circle of radius <math>15</math>. How many different chords of the circle contain <math>P</math> and have integer lengths?
+<math>\textbf{(A) } 11\qquad
+\textbf{(B) } 12\qquad
+\textbf{(C) } 13\qquad
+\textbf{(D) } 14\qquad
+\textbf{(E) } 29</math>
+[[1991 AHSME Problems/Problem 10|Solution]]
+== Problem 11 ==
+Jack and Jill run 10 km. They start at the same point, run 5 km up a hill, and return to the starting point by the same route. Jack has a 10 minute head start and runs at the rate of 15 km/hr uphill and 20 km/hr downhill. Jill runs 16 km/hr uphill and 22 km/hr downhill. How far from the top of the hill are they when they pass each other going in opposite directions (in km)?
+<math>\textbf{(A) } \frac{5}{4}\qquad
+\textbf{(B) } \frac{35}{27}\qquad
+\textbf{(C) } \frac{27}{20}\qquad
+\textbf{(D) } \frac{7}{3}\qquad
+\textbf{(E) } \frac{28}{49}</math>
+[[1991 AHSME Problems/Problem 11|Solution]]
+== Problem 12 ==
+The measures (in degrees) of the interior angles of a convex hexagon form an arithmetic sequence of integers. Let <math>m</math> be the measure of the largest interior angle of the hexagon. The largest possible value of <math>m</math>, in degrees, is
+<math>\textbf{(A) } 165\qquad
+\textbf{(B) } 167\qquad
+\textbf{(C) } 170\qquad
+\textbf{(D) } 175\qquad
+\textbf{(E) } 179</math>
+[[1991 AHSME Problems/Problem 12|Solution]]
+== Problem 13 ==
+Horses <math>X,Y</math> and <math>Z</math> are entered in a three-horse race in which ties are not possible. The odds against <math>X</math> winning are <math>3:1</math> and the odds against <math>Y</math> winning are <math>2:3</math>, what are the odds against <math>Z</math> winning? (By "odds against <math>H</math> winning are <math>p:q</math>" we mean the probability of <math>H</math> winning the race is <math>\frac{q}{p+q}</math>.)
+<math>\textbf{(A) } 3:20\qquad
+\textbf{(B) } 5:6\qquad
+\textbf{(C) } 8:5\qquad
+\textbf{(D) } 17:3\qquad
+\textbf{(E) } 20:3</math>
+[[1991 AHSME Problems/Problem 13|Solution]]
+== Problem 14 ==
+If <math>x</math> is the cube of a positive integer and <math>d</math> is the number of positive integers that are divisors of <math>x</math>, then <math>d</math> could be
+<math>\textbf{(A) } 200\qquad
+\textbf{(B) } 201\qquad
+\textbf{(C) } 202\qquad
+\textbf{(D) } 203\qquad
+\textbf{(E) } 204</math>
+[[1991 AHSME Problems/Problem 14|Solution]]
+== Problem 15 ==
+A circular table has 60 chairs around it. There are <math>N</math> people seated at this table in such a way that the next person seated must sit next to someone. What is the smallest possible value for <math>N</math>?
+<math>\textbf{(A) } 15\qquad
+\textbf{(B) } 20\qquad
+\textbf{(C) } 30\qquad
+\textbf{(D) } 40\qquad
+\textbf{(E) } 58</math>
+[[1991 AHSME Problems/Problem 15|Solution]]
+== Problem 16 ==
+One hundred students at Century High School participated in the AHSME last year, and their mean score was 100. The number of non-seniors taking the AHSME was <math>50\%</math> more than the number of seniors, and the mean score of the seniors was <math>50\%</math> higher than that of the non-seniors. What was the mean score of the seniors?
+<math>\textbf{(A) } 100\qquad
+\textbf{(B) } 112.5\qquad
+\textbf{(C) } 120\qquad
+\textbf{(D) } 125\qquad
+\textbf{(E) } 150</math>
+[[1991 AHSME Problems/Problem 16|Solution]]
+== Problem 17 ==
+A positive integer <math>N</math> is a ''palindrome'' if the integer obtained by reversing the sequence of digits of <math>N</math> is equal to <math>N</math>. The year 1991 is the only year in the current century with the following 2 properties:
+(a) It is a palindrome
+(b) It factors as a product of a 2-digit prime palindrome and a 3-digit prime palindrome.
+How many years in the millenium between 1000 and 2000 have properties (a) and (b)?
+<math>\textbf{(A) } 1\qquad
+\textbf{(B) } 2\qquad
+\textbf{(C) } 3\qquad
+\textbf{(D) } 4\qquad
+\textbf{(E) } 5</math>
+[[1991 AHSME Problems/Problem 17|Solution]]
+== Problem 18 ==
+If <math>S</math> is the set of points <math>z</math> in the complex plane such that <math>(3+4i)z</math> is a real number, then <math>S</math> is a
+<math>\textbf{(A) }</math> right triangle <math>\qquad \textbf{(B) }</math> circle <math>\qquad \textbf{(C) }</math> hyperbola <math>\qquad \textbf{(D) }</math> line <math>\qquad \textbf{(E) }</math> parabola
+[[1991 AHSME Problems/Problem 18|Solution]]
+== Problem 19 ==
+<asy>
+draw((0,0)--(0,3)--(4,0)--cycle,dot);
+draw((4,0)--(7,0)--(7,10)--cycle,dot);
+draw((0,3)--(7,10),dot);
+MP("C",(0,0),SW);MP("A",(0,3),NW);MP("B",(4,0),S);MP("E",(7,0),SE);MP("D",(7,10),NE);
+</asy>
+Triangle <math>ABC</math> has a right angle at <math>C, AC=3</math> and <math>BC=4</math>. Triangle <math>ABD</math> has a right angle at <math>A</math> and <math>AD=12</math>. Points <math>C</math> and <math>D</math> are on opposite sides of <math>\overline{AB}</math>. The line through <math>D</math> parallel to <math>\overline{AC}</math> meets <math>\overline{CB}</math> extended at <math>E</math>. If
+<cmath>\frac{DE}{DB}=\frac{m}{n},</cmath>
+where <math>m</math> and <math>n</math> are relatively prime positive integers, then <math>m+n</math> is
+<math>\textbf{(A) } 25\qquad
+\textbf{(B) } 128\qquad
+\textbf{(C) } 153\qquad
+\textbf{(D) } 243\qquad
+\textbf{(E) } 256</math>
+[[1991 AHSME Problems/Problem 19|Solution]]
+== Problem 20 ==
+The sum of all real <math>x</math> such that <math>(2^x-4)^3+(4^x-2)^3=(4^x+2^x-6)^3</math> is
+<math>\textbf{(A) } \frac32 \qquad \textbf{(B) } 2 \qquad \textbf{(C) } \frac52 \qquad \textbf{(D) } 3 \qquad \textbf{(E) } \frac72</math>
+[[1991 AHSME Problems/Problem 20|Solution]]
+== Problem 21 ==
+For all real numbers <math>x</math> except <math>x=0</math> and <math>x=1</math> the function <math>f(x)</math> is defined by <math>f(x/(x-1))=1/x</math>. Suppose <math>0\leq t\leq \pi/2</math>. What is the value of <math>f(\sec^2t)</math>?
+<math>\textbf{(A) } \sin^2\theta\qquad
+\textbf{(B) } \cos^2\theta\qquad
+\textbf{(C) } \tan^2\theta\qquad
+\textbf{(D) } \cot^2\theta\qquad
+\textbf{(E) } \csc^2\theta</math>
+[[1991 AHSME Problems/Problem 21|Solution]]
+== Problem 22 ==
+<asy>
+draw(circle((0,6sqrt(2)),2sqrt(2)),black+linewidth(.75));
+draw(circle((0,3sqrt(2)),sqrt(2)),black+linewidth(.75));
+draw((-8/3,16sqrt(2)/3)--(-4/3,8sqrt(2)/3)--(0,0)--(4/3,8sqrt(2)/3)--(8/3,16sqrt(2)/3),dot);
+MP("B",(-8/3,16*sqrt(2)/3),W);MP("B'",(8/3,16*sqrt(2)/3),E);
+MP("A",(-4/3,8*sqrt(2)/3),W);MP("A'",(4/3,8*sqrt(2)/3),E);
+MP("P",(0,0),S);
+</asy>
+Two circles are externally tangent. Lines <math>\overline{PAB}</math> and <math>\overline{PA'B'}</math> are common tangents with <math>A</math> and <math>A'</math> on the smaller circle <math>B</math> and <math>B'</math> on the larger circle. If <math>PA=AB=4</math>, then the area of the smaller circle is
+<math>\textbf{(A) } 1.44\pi\qquad
+\textbf{(B) } 2\pi\qquad
+\textbf{(C) } 2.56\pi\qquad
+\textbf{(D) } \sqrt{8}\pi\qquad
+\textbf{(E) } 4\pi</math>
+[[1991 AHSME Problems/Problem 22|Solution]]
+== Problem 23 ==
+<asy>
+draw((0,0)--(0,2)--(2,2)--(2,0)--cycle,dot);
+draw((2,2)--(0,0)--(0,1)--cycle,dot);
+draw((0,2)--(1,0),dot);
+MP("B",(0,0),SW);MP("A",(0,2),NW);MP("D",(2,2),NE);MP("C",(2,0),SE);
+MP("E",(0,1),W);MP("F",(1,0),S);MP("H",(2/3,2/3),E);MP("I",(2/5,6/5),N);
+dot((1,0));dot((0,1));dot((2/3,2/3));dot((2/5,6/5));
+</asy>
+If <math>ABCD</math> is a <math>2\times2</math> square, <math>E</math> is the midpoint of <math>\overline{AB}</math>,<math>F</math> is the midpoint of <math>\overline{BC}</math>,<math>\overline{AF}</math> and <math>\overline{DE}</math> intersect at <math>I</math>, and <math>\overline{BD}</math> and <math>\overline{AF}</math> intersect at <math>H</math>, then the area of quadrilateral <math>BEIH</math> is
+<math>\textbf{(A) } \frac{1}{3}\qquad
+\textbf{(B) } \frac{2}{5}\qquad
+\textbf{(C) } \frac{7}{15}\qquad
+\textbf{(D) } \frac{8}{15}\qquad
+\textbf{(E) } \frac{3}{5}</math>
+[[1991 AHSME Problems/Problem 23|Solution]]
+== Problem 24 ==
+The graph, <math>G</math> of <math>y=\log_{10}x</math> is rotated <math>90^{\circ}</math> counter-clockwise about the origin to obtain a new graph <math>G'</math>. Which of the following is an equation for <math>G'</math>?
+<math>\textbf{(A) } y=\log_{10}\left(\frac{x+90}{9}\right) \qquad
+\textbf{(B) } y=\log_{x}10 \qquad
+\textbf{(C) } y=\frac{1}{x+1} \qquad
+\textbf{(D) } y=10^{-x} \qquad
+\textbf{(E) } y=10^x</math>
+[[1991 AHSME Problems/Problem 24|Solution]]
+== Problem 25 ==
+If <math>T_n=1+2+3+\cdots +n</math> and
+<cmath>P_n=\frac{T_2}{T_2-1}\cdot\frac{T_3}{T_3-1}\cdot\frac{T_4}{T_4-1}\cdot\cdots\cdot\frac{T_n}{T_n-1}</cmath>
+for <math>n=2,3,4,\cdots,</math> then <math>P_{1991}</math> is closest to which of the following numbers?
+<math>\textbf{(A) } 2.0\qquad
+\textbf{(B) } 2.3\qquad
+\textbf{(C) } 2.6\qquad
+\textbf{(D) } 2.9\qquad
+\textbf{(E) } 3.2</math>
+[[1991 AHSME Problems/Problem 25|Solution]]
+== Problem 26 ==
+An <math>n</math>-digit positive integer is cute if its <math>n</math> digits are an arrangement of the set <math>\{1,2,...,n\}</math> and its first
+<math>k</math> digits form an integer that is divisible by <math>k</math>  , for  <math>k  = 1,2,...,n</math>. For example, <math>321</math> is a cute <math>3</math>-digit integer because <math>1</math> divides <math>3</math>, <math>2</math> divides <math>32</math>, and <math>3</math> divides <math>321</math>. How many cute <math>6</math>-digit integers are there?
+<math>\textbf{(A) } 0\qquad
+\textbf{(B) } 1\qquad
+\textbf{(C) } 2\qquad
+\textbf{(D) } 3\qquad
+\textbf{(E) } 4</math>
+[[1991 AHSME Problems/Problem 26|Solution]]
+== Problem 27 ==
+If <cmath>x+\sqrt{x^2-1}+\frac{1}{x-\sqrt{x^2-1}}=20,</cmath> then <cmath>x^2+\sqrt{x^4-1}+\frac{1}{x^2+\sqrt{x^4-1}}=</cmath>
+<math>\textbf{(A) } 5.05 \qquad
+\textbf{(B) } 20 \qquad
+\textbf{(C) } 51.005 \qquad
+\textbf{(D) } 61.25 \qquad
+\textbf{(E) } 400</math>
+[[1991 AHSME Problems/Problem 27|Solution]]
+== Problem 28 ==
+Initially an urn contains 100 white and 100 black marbles. Repeatedly 3 marbles are removed (at random) from the urn and replaced with some marbles from a pile outside the urn as follows: 3 blacks are replaced with 1 black, or 2 blacks and 1 white are replaced with a white and a black, or 1 black and 2 whites are replaced with 2 whites, or 3 whites are replaced with a black and a white. Which of the following could be the contents of the urn after repeated applications of this procedure?
+<math>\textbf{(A) }</math> 2 black <math>\qquad \textbf{(B) }</math> 2 white <math>\qquad \textbf{(C) }</math> 1 black <math>\qquad \textbf{(D) }</math> 1 black and 1 white <math>\qquad \textbf{(E) }</math> 1 white
+[[1991 AHSME Problems/Problem 28|Solution]]
+== Problem 29 ==
+Equilateral triangle <math>ABC</math> has <math>P</math> on <math>AB</math> and <math>Q</math> on <math>AC</math>. The triangle is folded along <math>PQ</math> so that vertex <math>A</math> now rests at <math>A'</math> on side <math>BC</math>. If <math>BA'=1</math> and <math>A'C=2</math> then the length of the crease <math>PQ</math> is
+<math>\textbf{(A) } \frac{8}{5} \qquad
+\textbf{(B) } \frac{7}{20}\sqrt{21} \qquad
+\textbf{(C) } \frac{1+\sqrt{5}}{2} \qquad
+\textbf{(D) } \frac{13}{8} \qquad
+\textbf{(E) } \sqrt{3}</math>
+[[1991 AHSME Problems/Problem 29|Solution]]
+== Problem 30 ==
+For any set <math>S</math>, let <math>|S|</math> denote the number of elements in <math>S</math>, and let <math>n(S)</math> be the number of subsets of <math>S</math>, including the empty set and the set <math>S</math> itself. If <math>A</math>, <math>B</math>, and <math>C</math> are sets for which <math>n(A)+n(B)+n(C)=n(A\cup B\cup C)</math> and <math>|A|=|B|=100</math>, then what is the minimum possible value of <math>|A\cap B\cap C|</math>?
+<math>\textbf{(A) } 96 \qquad \textbf{(B) } 97 \qquad \textbf{(C) } 98 \qquad \textbf{(D) } 99 \qquad \textbf{(E) } 100</math>
+[[1991 AHSME Problems/Problem 30|Solution]]
+== See also ==
+* [[AMC 12 Problems and Solutions]]
+* [[Mathematics competition resources]]
+{{AHSME box|year=1991|before=[[1990 AHSME]]|after=[[1992 AHSME]]}}
+{{MAA Notice}}