Difference between revisions of "1980 AHSME Problems"

Latest revision as of 09:47, 30 April 2021

1980 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.
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

The largest whole number such that seven times the number is less than $100$ is

$\text{(A)} \ 12 \qquad \text{(B)} \ 13 \qquad \text{(C)} \ 14 \qquad \text{(D)} \ 15 \qquad \text{(E)} \ 16$

Solution

Problem 2

The degree of $(x^2+1)^4 (x^3+1)^3$ as a polynomial in $x$ is

$\text{(A)} \ 5 \qquad \text{(B)} \ 7 \qquad \text{(C)} \ 12 \qquad \text{(D)} \ 17 \qquad \text{(E)} \ 72$

Solution

Problem 3

If the ratio of $2x-y$ to $x+y$ is $\frac{2}{3}$ , what is the ratio of $x$ to $y$ ?

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

Solution

Problem 4

In the adjoining figure, CDE is an equilateral triangle and ABCD and DEFG are squares. The measure of $\angle GDA$ is

$\text{(A)} \ 90^\circ \qquad \text{(B)} \ 105^\circ \qquad \text{(C)} \ 120^\circ \qquad \text{(D)} \ 135^\circ \qquad \text{(E)} \ 150^\circ$

$[asy] defaultpen(linewidth(0.7)+fontsize(10)); pair D=origin, C=D+dir(240), E=D+dir(300), F=E+dir(30), G=D+dir(30), A=D+dir(150), B=C+dir(150); draw(E--D--G--F--E--C--D--A--B--C); pair point=(0,0.5); label("$A$", A, dir(point--A)); label("$B$", B, dir(point--B)); label("$C$", C, dir(point--C)); label("$D$", D, dir(-15)); label("$E$", E, dir(point--E)); label("$F$", F, dir(point--F)); label("$G$", G, dir(point--G));[/asy]$

Solution

Problem 5

If $AB$ and $CD$ are perpendicular diameters of circle $Q$ , $P$ in $\overline{AQ}$ , and $\measuredangle QPC = 60^\circ$ , then the length of $PQ$ divided by the length of $AQ$ is

$[asy] defaultpen(linewidth(0.7)+fontsize(10)); pair A=(-1,0), B=(1,0), C=(0,1), D=(0,-1), Q=origin, P=(-0.5,0); draw(P--C--D^^A--B^^Circle(Q,1)); label("$A$", A, W); label("$B$", B, E); label("$C$", C, N); label("$D$", D, S); label("$P$", P, S); label("$Q$", Q, SE); label("$60^\circ$", P+0.05*dir(30), dir(30));[/asy]$

$\text{(A)} \ \frac{\sqrt{3}}{2} \qquad \text{(B)} \ \frac{\sqrt{3}}{3} \qquad \text{(C)} \ \frac{\sqrt{2}}{2} \qquad \text{(D)} \ \frac12 \qquad \text{(E)} \ \frac23$

Solution

Problem 6

A positive number $x$ satisfies the inequality $\sqrt{x} < 2x$ if and only if

$\text{(A)} \ x > \frac{1}{4} \qquad \text{(B)} \ x > 2 \qquad \text{(C)} \ x > 4 \qquad \text{(D)} \ x < \frac{1}{4}\qquad \text{(E)} \ x < 4$

Solution

Problem 7

Sides $AB,BC,CD$ and $DA$ of convex polygon $ABCD$ have lengths 3,4,12, and 13, respectively, and $\measuredangle CBA$ is a right angle. The area of the quadrilateral is

$[asy] defaultpen(linewidth(0.7)+fontsize(10)); real r=degrees((12,5)), s=degrees((3,4)); pair D=origin, A=(13,0), C=D+12*dir(r), B=A+3*dir(180-(90-r+s)); draw(A--B--C--D--cycle); markscalefactor=0.05; draw(rightanglemark(A,B,C)); pair point=incenter(A,C,D); label("$A$", A, dir(point--A)); label("$B$", B, dir(point--B)); label("$C$", C, dir(point--C)); label("$D$", D, dir(point--D)); label("$3$", A--B, dir(A--B)*dir(-90)); label("$4$", B--C, dir(B--C)*dir(-90)); label("$12$", C--D, dir(C--D)*dir(-90)); label("$13$", D--A, dir(D--A)*dir(-90));[/asy]$

$\text{(A)} \ 32 \qquad \text{(B)} \ 36 \qquad \text{(C)} \ 39 \qquad \text{(D)} \ 42 \qquad \text{(E)} \ 48$

Solution

Problem 8

How many pairs $(a,b)$ of non-zero real numbers satisfy the equation

$\frac{1}{a} + \frac{1}{b} = \frac{1}{a+b}$ $\text{(A)} \ \text{none} \qquad \text{(B)} \ 1 \qquad \text{(C)} \ 2 \qquad \text{(D)} \ \text{one pair for each} ~b \neq 0$ $\text{(E)} \ \text{two pairs for each} ~b \neq 0$

Solution

Problem 9

A man walks $x$ miles due west, turns $150^\circ$ to his left and walks 3 miles in the new direction. If he finishes a a point $\sqrt{3}$ from his starting point, then $x$ is

$\text{(A)} \ \sqrt 3 \qquad \text{(B)} \ 2\sqrt{5} \qquad \text{(C)} \ \frac 32 \qquad \text{(D)} \ 3 \qquad \text{(E)} \ \text{not uniquely determined}$

Solution

Problem 10

The number of teeth in three meshed gears $A$ , $B$ , and $C$ are $x$ , $y$ , and $z$ , respectively. (The teeth on all gears are the same size and regularly spaced.) The angular speeds, in revolutions per minutes of $A$ , $B$ , and $C$ are in the proportion

$\text{(A)} \ x: y: z ~~\text{(B)} \ z: y: x ~~ \text{(C)} \ y: z: x~~ \text{(D)} \ yz: xz: xy ~~ \text{(E)} \ xz: yx: zy$

Solution

Problem 11

If the sum of the first $10$ terms and the sum of the first $100$ terms of a given arithmetic progression are $100$ and $10$ , respectively, then the sum of first $110$ terms is:

$\text{(A)} \ 90 \qquad \text{(B)} \ -90 \qquad \text{(C)} \ 110 \qquad \text{(D)} \ -110 \qquad \text{(E)} \ -100$

Solution

Problem 12

The equations of $L_1$ and $L_2$ are $y=mx$ and $y=nx$ , respectively. Suppose $L_1$ makes twice as large of an angle with the horizontal (measured counterclockwise from the positive x-axis ) as does $L_2$ , and that $L_1$ has 4 times the slope of $L_2$ . If $L_1$ is not horizontal, then $mn$ is

$\text{(A)} \ \frac{\sqrt{2}}{2} \qquad \text{(B)} \ -\frac{\sqrt{2}}{2} \qquad \text{(C)} \ 2 \qquad \text{(D)} \ -2 \qquad \text{(E)} \ \text{not uniquely determined}$

Solution

Problem 13

A bug (of negligible size) starts at the origin on the coordinate plane. First, it moves one unit right to $(1,0)$ . Then it makes a $90^\circ$ counterclockwise and travels $\frac 12$ a unit to $\left(1, \frac 12 \right)$ . If it continues in this fashion, each time making a $90^\circ$ degree turn counterclockwise and traveling half as far as the previous move, to which of the following points will it come closest?

$\text{(A)} \ \left(\frac 23, \frac 23 \right) \qquad \text{(B)} \ \left( \frac 45, \frac 25 \right) \qquad \text{(C)} \ \left( \frac 23, \frac 45 \right) \qquad \text{(D)} \ \left(\frac 23, \frac 13 \right) \qquad \text{(E)} \ \left(\frac 25, \frac 45 \right)$

Solution

Problem 14

If the function $f$ is defined by $f(x)=\frac{cx}{2x+3} ,\quad x\neq -\frac{3}{2} ,$ satisfies $x=f(f(x))$ for all real numbers $x$ except $-\frac{3}{2}$ , then $c$ is

$\text{(A)} \ -3 \qquad \text{(B)} \ - \frac{3}{2} \qquad \text{(C)} \ \frac{3}{2} \qquad \text{(D)} \ 3 \qquad \text{(E)} \ \text{not uniquely determined}$

Solution

Problem 15

A store prices an item in dollars and cents so that when 4% sales tax is added, no rounding is necessary because the result is exactly $n$ dollars where $n$ is a positive integer. The smallest value of $n$ is

$\text{(A)} \ 1 \qquad \text{(B)} \ 13 \qquad \text{(C)} \ 25 \qquad \text{(D)} \ 26 \qquad \text{(E)} \ 100$

Solution

Problem 16

Four of the eight vertices of a cube are the vertices of a regular tetrahedron. Find the ratio of the surface area of the cube to the surface area of the tetrahedron.

$\text{(A)} \ \sqrt 2 \qquad \text{(B)} \ \sqrt 3 \qquad \text{(C)} \ \sqrt{\frac{3}{2}} \qquad \text{(D)} \ \frac{2}{\sqrt{3}} \qquad \text{(E)} \ 2$

Solution

Problem 17

Given that $i^2=-1$ , for how many integers $n$ is $(n+i)^4$ an integer?

$\text{(A)} \ \text{none} \qquad \text{(B)} \ 1 \qquad \text{(C)} \ 2 \qquad \text{(D)} \ 3 \qquad \text{(E)} \ 4$

Solution

Problem 18

If $b>1$ , $\sin x>0$ , $\cos x>0$ , and $\log_b \sin x = a$ , then $\log_b \cos x$ equals

$\text{(A)} \ 2\log_b(1-b^{a/2}) ~~\text{(B)} \ \sqrt{1-a^2} ~~\text{(C)} \ b^{a^2} ~~\text{(D)} \ \frac 12 \log_b(1-b^{2a}) ~~\text{(E)} \ \text{none of these}$

Solution

Problem 19

Let $C_1, C_2$ and $C_3$ be three parallel chords of a circle on the same side of the center. The distance between $C_1$ and $C_2$ is the same as the distance between $C_2$ and $C_3$ . The lengths of the chords are $20, 16$ , and $8$ . The radius of the circle is

$\text{(A)} \ 12 \qquad \text{(B)} \ 4\sqrt{7} \qquad \text{(C)} \ \frac{5\sqrt{65}}{3} \qquad \text{(D)}\ \frac{5\sqrt{22}}{2}\qquad \text{(E)}\ \text{not uniquely determined}$

Solution

Problem 20

A box contains $2$ pennies, $4$ nickels, and $6$ dimes. Six coins are drawn without replacement, with each coin having an equal probability of being chosen. What is the probability that the value of coins drawn is at least $50$ cents?

$\text{(A)} \ \frac{37}{924} \qquad \text{(B)} \ \frac{91}{924} \qquad \text{(C)} \ \frac{127}{924} \qquad \text{(D)}\ \frac{132}{924}\qquad \text{(E)}\ \text{none of these}$

Solution

Problem 21

$[asy] defaultpen(linewidth(0.7)+fontsize(10)); pair B=origin, C=(15,3), D=(5,1), A=7*dir(72)*dir(B--C), E=midpoint(A--C), F=intersectionpoint(A--D, B--E); draw(E--B--A--C--B^^A--D); label("$A$", A, dir(D--A)); label("$B$", B, dir(E--B)); label("$C$", C, dir(0)); label("$D$", D, SE); label("$E$", E, N); label("$F$", F, dir(80));[/asy]$

In triangle $ABC$ , $\measuredangle CBA=72^\circ$ , $E$ is the midpoint of side $AC$ , and $D$ is a point on side $BC$ such that $2BD=DC$ ; $AD$ and $BE$ intersect at $F$ . The ratio of the area of triangle $BDF$ to the area of quadrilateral $FDCE$ is

$\text{(A)} \ \frac 15 \qquad \text{(B)} \ \frac 14 \qquad \text{(C)} \ \frac 13 \qquad \text{(D)}\ \frac{2}{5}\qquad \text{(E)}\ \text{none of these}$

Solution

Problem 22

For each real number $x$ , let $f(x)$ be the minimum of the numbers $4x+1, x+2$ , and $-2x+4$ . Then the maximum value of $f(x)$ is

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

Solution

Problem 23

Line segments drawn from the vertex opposite the hypotenuse of a right triangle to the points trisecting the hypotenuse have lengths $\sin x$ and $\cos x$ , where $x$ is a real number such that $0<x<\frac{\pi}{2}$ . The length of the hypotenuse is

$\text{(A)} \ \frac{4}{3} \qquad \text{(B)} \ \frac{3}{2} \qquad \text{(C)} \ \frac{3\sqrt{5}}{5} \qquad \text{(D)}\ \frac{2\sqrt{5}}{3}\qquad \text{(E)}\ \text{not uniquely determined}$

Solution

Problem 24

For some real number $r$ , the polynomial $8x^3-4x^2-42x+45$ is divisible by $(x-r)^2$ . Which of the following numbers is closest to $r$ ?

$\text{(A)} \ 1.22 \qquad \text{(B)} \ 1.32 \qquad \text{(C)} \ 1.42 \qquad \text{(D)} \ 1.52 \qquad \text{(E)} \ 1.62$

Solution

Problem 25

In the non-decreasing sequence of odd integers $\{a_1,a_2,a_3,\ldots \}=\{1,3,3,3,5,5,5,5,5,\ldots \}$ each odd positive integer $k$ appears $k$ times. It is a fact that there are integers $b, c$ , and $d$ such that for all positive integers $n$ , $a_n=b\lfloor \sqrt{n+c} \rfloor +d$ , where $\lfloor x \rfloor$ denotes the largest integer not exceeding $x$ . The sum $b+c+d$ equals

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

Solution

Problem 26

Four balls of radius $1$ are mutually tangent, three resting on the floor and the fourth resting on the others. A tetrahedron, each of whose edges have length $s$ , is circumscribed around the balls. Then $s$ equals

$\text{(A)} \ 4\sqrt 2 \qquad \text{(B)} \ 4\sqrt 3 \qquad \text{(C)} \ 2\sqrt 6 \qquad \text{(D)}\ 1+2\sqrt 6\qquad \text{(E)}\ 2+2\sqrt 6$

Solution

Problem 27

The sum $\sqrt[3] {5+2\sqrt{13}}+\sqrt[3]{5-2\sqrt{13}}$ equals

$\text{(A)} \ \frac 32 \qquad \text{(B)} \ \frac{\sqrt[3]{65}}{4} \qquad \text{(C)} \ \frac{1+\sqrt[6]{13}}{2} \qquad \text{(D)}\ \sqrt[3]{2}\qquad \text{(E)}\ \text{none of these}$

Solution

Problem 28

The polynomial $x^{2n}+1+(x+1)^{2n}$ is not divisible by $x^2+x+1$ if $n$ equals

$\text{(A)} \ 17 \qquad \text{(B)} \ 20 \qquad \text{(C)} \ 21 \qquad \text{(D)} \ 64 \qquad \text{(E)} \ 65$

Solution

Problem 29

How many ordered triples (x,y,z) of integers satisfy the system of equations below?

$\begin{array}{l} x^2-3xy+2y^2-z^2=31 \\ -x^2+6yz+2z^2=44 \\ x^2+xy+8z^2=100\\ \end{array}$

$\text{(A)} \ 0 \qquad \text{(B)} \ 1 \qquad \text{(C)} \ 2 \qquad \text{(D)}\ \text{a finite number greater than 2}\qquad \text{(E)}\ \text{infinitely many}$

Solution

Problem 30

A six digit number (base 10) is squarish if it satisfies the following conditions:

(i) none of its digits are zero;

(ii) it is a perfect square; and

(iii) the first of two digits, the middle two digits and the last two digits of the number are all perfect squares when considered as two digit numbers.

How many squarish numbers are there?

$\text{(A)} \ 0 \qquad \text{(B)} \ 2 \qquad \text{(C)} \ 3 \qquad \text{(D)} \ 8 \qquad \text{(E)} \ 9$

Solution

1980 AHSME (Problems • Answer Key • Resources)
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Difference between revisions of "1980 AHSME Problems"

Latest revision as of 09:47, 30 April 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: @@
+{{AHSME Problems
+|year = 1980
+}}
 == Problem 1 ==
-The largest whole number such that seven times the number is less than 100 is
+The largest whole number such that seven times the number is less than <math>100</math> is
 <math>\text{(A)} \ 12 \qquad \text{(B)} \ 13 \qquad \text{(C)} \ 14 \qquad \text{(D)} \ 15 \qquad \text{(E)} \ 16</math>
@@ Line 30: / Line 33: @@
 draw(E--D--G--F--E--C--D--A--B--C);
 pair point=(0,0.5);
-label("<math>A</math>", A, dir(point--A));
+label("$A$", A, dir(point--A));
-label("<math>B</math>", B, dir(point--B));
+label("$B$", B, dir(point--B));
-label("<math>C</math>", C, dir(point--C));
+label("$C$", C, dir(point--C));
-label("<math>D</math>", D, dir(-15));
+label("$D$", D, dir(-15));
-label("<math>E</math>", E, dir(point--E));
+label("$E$", E, dir(point--E));
-label("<math>F</math>", F, dir(point--F));
+label("$F$", F, dir(point--F));
-label("<math>G</math>", G, dir(point--G));
+label("$G$", G, dir(point--G));</asy>
-<\asy>
 [[1980 AHSME Problems/Problem 4|Solution]]
@@ Line 44: / Line 46: @@
 If <math>AB</math> and <math>CD</math> are perpendicular diameters of circle <math>Q</math>, <math>P</math> in <math>\overline{AQ}</math>, and <math>\measuredangle QPC = 60^\circ</math>, then the length of <math>PQ</math> divided by the length of <math>AQ</math> is
-[asy]
+<asy>
 defaultpen(linewidth(0.7)+fontsize(10));
 pair A=(-1,0), B=(1,0), C=(0,1), D=(0,-1), Q=origin, P=(-0.5,0);
 draw(P--C--D^^A--B^^Circle(Q,1));
-label("<math>A</math>", A, W);
+label("$A$", A, W);
-label("<math>B</math>", B, E);
+label("$B$", B, E);
-label("<math>C</math>", C, N);
+label("$C$", C, N);
-label("<math>D</math>", D, S);
+label("$D$", D, S);
-label("<math>P</math>", P, S);
+label("$P$", P, S);
-label("<math>Q</math>", Q, SE);
+label("$Q$", Q, SE);
-label("<math>60^\circ</math>", P+0.0.5*dir(30), dir(30));[/asy]
+label("$60^\circ$", P+0.05*dir(30), dir(30));</asy>
 <math> \text{(A)} \ \frac{\sqrt{3}}{2} \qquad \text{(B)} \ \frac{\sqrt{3}}{3} \qquad \text{(C)} \ \frac{\sqrt{2}}{2} \qquad \text{(D)} \ \frac12 \qquad \text{(E)} \ \frac23 </math>
@@ Line 63: / Line 65: @@
 A positive number <math>x</math> satisfies the inequality <math>\sqrt{x} < 2x</math> if and only if
-<math>\text{(A)} \ x > \frac{1}{4} \qquad \text{(B)} \ x > 2 \qquad \text{(C)} \x > 4 \qquad \text{(D)} \ x < \frac{1}{4}\qquad \text{(E)} \x < 4</math>
+<math>\text{(A)} \ x > \frac{1}{4} \qquad \text{(B)} \ x > 2 \qquad \text{(C)} \ x > 4 \qquad \text{(D)} \ x < \frac{1}{4}\qquad \text{(E)} \ x < 4</math>
 [[1980 AHSME Problems/Problem 6|Solution]]
@@ Line 70: / Line 72: @@
 Sides <math>AB,BC,CD</math> and <math>DA</math> of convex polygon <math>ABCD</math> have lengths 3,4,12, and 13, respectively, and <math>\measuredangle CBA</math> is a right angle. The area of the quadrilateral is
-[asy]
+<asy>
 defaultpen(linewidth(0.7)+fontsize(10));
 real r=degrees((12,5)), s=degrees((3,4));
@@ Line 78: / Line 80: @@
 draw(rightanglemark(A,B,C));
 pair point=incenter(A,C,D);
-label("<math>A</math>", A, dir(point--A));
+label("$A$", A, dir(point--A));
-label("<math>B</math>", B, dir(point--B));
+label("$B$", B, dir(point--B));
-label("<math>C</math>", C, dir(point--C));
+label("$C$", C, dir(point--C));
-label("<math>D</math>", D, dir(point--D));
+label("$D$", D, dir(point--D));
-label("<math>3</math>", A--B, dir(A--B)*dir(-90));
+label("$3$", A--B, dir(A--B)*dir(-90));
-label("<math>4</math>", B--C, dir(B--C)*dir(-90));
+label("$4$", B--C, dir(B--C)*dir(-90));
-label("<math>12</math>", C--D, dir(C--D)*dir(-90));
+label("$12$", C--D, dir(C--D)*dir(-90));
-label("<math>13</math>", D--A, dir(D--A)*dir(-90));[/asy]
+label("$13$", D--A, dir(D--A)*dir(-90));</asy>
 <math>\text{(A)} \ 32 \qquad \text{(B)} \ 36 \qquad \text{(C)} \ 39 \qquad \text{(D)} \ 42 \qquad \text{(E)} \ 48</math>
@@ Line 118: / Line 120: @@
 == Problem 11 ==
-If the sum of the first 10 terms and the sum of the first 100 terms of a given arithmetic progression are 100 and 10, respectively, then the sum of first 110 terms is:
+If the sum of the first <math>10</math> terms and the sum of the first <math>100</math> terms of a given arithmetic progression are <math>100</math> and <math>10</math>,
+respectively, then the sum of first <math>110</math> terms is:
 <math>\text{(A)} \ 90 \qquad \text{(B)} \ -90 \qquad \text{(C)} \ 110 \qquad \text{(D)} \ -110 \qquad \text{(E)} \ -100</math>
@@ Line 141: / Line 144: @@
 == Problem 14 ==
 If the function <math>f</math> is defined by
-<cmath> f(x)=\frac{cx}{2x+3} , ~~~x\neq -\frac 32 ,  </cmath> satisfies <math>x=f(f(x))</math> for all rea numbers <math>x</math> except <math>-\frac 32</math>, then <math>c</math> is
+<cmath> f(x)=\frac{cx}{2x+3} ,\quad x\neq -\frac{3}{2} ,  </cmath>
-<math>\text{(A)} \ -3 \qquad \text{(B)} \ - \frac{3}{2} \qquad \text{(C)} \ \frac{3}{2} \qquad \text{(D)} \ 3 \qquad \text{(E)} \ \text{not uniquely determined}</math>
+satisfies <math>x=f(f(x))</math> for all real numbers <math>x</math> except <math>-\frac{3}{2}</math>, then <math>c</math> is
+<math>\text{(A)} \ -3 \qquad
+\text{(B)} \ - \frac{3}{2} \qquad
+\text{(C)} \ \frac{3}{2} \qquad
+\text{(D)} \ 3 \qquad
+\text{(E)} \ \text{not uniquely determined}</math>
 [[1980 AHSME Problems/Problem 14|Solution]]
@@ Line 175: / Line 185: @@
 [[1980 AHSME Problems/Problem 18|Solution]]
-== Problem 19 ==
+==Problem 19==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+Let <math>C_1, C_2</math> and <math>C_3</math> be three parallel chords of a circle on the same side of the center.
+The distance between <math>C_1</math> and <math>C_2</math> is the same as the distance between <math>C_2</math> and <math>C_3</math>.
+The lengths of the chords are <math>20, 16</math>, and <math>8</math>. The radius of the circle is
+<math>\text{(A)} \ 12 \qquad
+\text{(B)} \ 4\sqrt{7} \qquad
+\text{(C)} \ \frac{5\sqrt{65}}{3} \qquad
+\text{(D)}\ \frac{5\sqrt{22}}{2}\qquad
+\text{(E)}\ \text{not uniquely determined}  </math>
 [[1980 AHSME Problems/Problem 19|Solution]]
+==Problem 20==
+A box contains <math>2</math> pennies, <math>4</math> nickels, and <math>6</math> dimes. Six coins are drawn without replacement,
+with each coin having an equal probability of being chosen. What is the probability that the value of coins drawn is at least <math>50</math> cents?
-== Problem 20 ==
+<math>\text{(A)} \ \frac{37}{924} \qquad
+\text{(B)} \ \frac{91}{924} \qquad
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+\text{(C)} \ \frac{127}{924} \qquad
+\text{(D)}\ \frac{132}{924}\qquad
+\text{(E)}\ \text{none of these} </math>
 [[1980 AHSME Problems/Problem 20|Solution]]
-== Problem 21 ==
+==Problem 21==
+<asy>
+defaultpen(linewidth(0.7)+fontsize(10));
+pair B=origin, C=(15,3), D=(5,1), A=7*dir(72)*dir(B--C), E=midpoint(A--C), F=intersectionpoint(A--D, B--E);
+draw(E--B--A--C--B^^A--D);
+label("$A$", A, dir(D--A));
+label("$B$", B, dir(E--B));
+label("$C$", C, dir(0));
+label("$D$", D, SE);
+label("$E$", E, N);
+label("$F$", F, dir(80));</asy>
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+In triangle <math>ABC</math>, <math>\measuredangle CBA=72^\circ</math>, <math>E</math> is the midpoint of side <math>AC</math>,
+and <math>D</math> is a point on side <math>BC</math> such that <math>2BD=DC</math>; <math>AD</math> and <math>BE</math> intersect at <math>F</math>.
+The ratio of the area of triangle <math>BDF</math> to the area of quadrilateral <math>FDCE</math> is
+<math>\text{(A)} \ \frac 15 \qquad
+\text{(B)} \ \frac 14 \qquad
+\text{(C)} \ \frac 13 \qquad
+\text{(D)}\ \frac{2}{5}\qquad
+\text{(E)}\ \text{none of these}</math>
 [[1980 AHSME Problems/Problem 21|Solution]]
-== Problem 22 ==
+==Problem 22==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+For each real number <math>x</math>, let <math>f(x)</math> be the minimum of the numbers <math>4x+1, x+2</math>, and <math>-2x+4</math>. Then the maximum value of <math>f(x)</math> is
+<math>\text{(A)} \ \frac{1}{3} \qquad
+\text{(B)} \ \frac{1}{2} \qquad
+\text{(C)} \ \frac{2}{3} \qquad
+\text{(D)} \ \frac{5}{2} \qquad
+\text{(E)}\ \frac{8}{3}  </math>
 [[1980 AHSME Problems/Problem 22|Solution]]
-== Problem 23 ==
+==Problem 23==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+Line segments drawn from the vertex opposite the hypotenuse of a right triangle to the points trisecting the hypotenuse have lengths <math>\sin x</math> and <math>\cos x</math>, where <math>x</math> is a real number such that <math>0<x<\frac{\pi}{2}</math>. The length of the hypotenuse is
+<math>\text{(A)} \ \frac{4}{3} \qquad
+\text{(B)} \ \frac{3}{2} \qquad
+\text{(C)} \ \frac{3\sqrt{5}}{5} \qquad
+\text{(D)}\ \frac{2\sqrt{5}}{3}\qquad
+\text{(E)}\ \text{not uniquely determined}</math>
 [[1980 AHSME Problems/Problem 23|Solution]]
-== Problem 24 ==
+==Problem 24==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+For some real number <math>r</math>, the polynomial <math>8x^3-4x^2-42x+45</math> is divisible by <math>(x-r)^2</math>. Which of the following numbers is closest to <math>r</math>?
+<math>\text{(A)} \ 1.22 \qquad
+\text{(B)} \ 1.32 \qquad
+\text{(C)} \ 1.42 \qquad
+\text{(D)} \ 1.52 \qquad
+\text{(E)} \ 1.62  </math>
 [[1980 AHSME Problems/Problem 24|Solution]]
-== Problem 25 ==
+==Problem 25==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+In the non-decreasing sequence of odd integers <math>\{a_1,a_2,a_3,\ldots \}=\{1,3,3,3,5,5,5,5,5,\ldots \}</math> each odd positive integer <math>k</math>
+appears <math>k</math> times. It is a fact that there are integers <math>b, c</math>, and <math>d</math> such that for all positive integers <math>n</math>,
+<math>a_n=b\lfloor \sqrt{n+c} \rfloor +d</math>,
+where <math>\lfloor x \rfloor</math> denotes the largest integer not exceeding <math>x</math>. The sum <math>b+c+d</math> equals
+<math>\text{(A)} \ 0 \qquad
+\text{(B)} \ 1 \qquad
+\text{(C)} \ 2 \qquad
+\text{(D)} \ 3 \qquad
+\text{(E)} \ 4    </math>
 [[1980 AHSME Problems/Problem 25|Solution]]
-== Problem 26 ==
+==Problem 26==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+Four balls of radius <math>1</math> are mutually tangent, three resting on the floor and the fourth resting on the others.
+A tetrahedron, each of whose edges have length <math>s</math>, is circumscribed around the balls. Then <math>s</math> equals
+<math>\text{(A)} \ 4\sqrt 2 \qquad
+\text{(B)} \ 4\sqrt 3 \qquad
+\text{(C)} \ 2\sqrt 6 \qquad
+\text{(D)}\ 1+2\sqrt 6\qquad
+\text{(E)}\ 2+2\sqrt 6</math>
 [[1980 AHSME Problems/Problem 26|Solution]]
-== Problem 27 ==
+==Problem 27==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+The sum <math>\sqrt[3] {5+2\sqrt{13}}+\sqrt[3]{5-2\sqrt{13}}</math> equals
+<math>\text{(A)} \ \frac 32 \qquad
+\text{(B)} \ \frac{\sqrt[3]{65}}{4} \qquad
+\text{(C)} \ \frac{1+\sqrt[6]{13}}{2} \qquad
+\text{(D)}\ \sqrt[3]{2}\qquad
+\text{(E)}\ \text{none of these} </math>
 [[1980 AHSME Problems/Problem 27|Solution]]
-== Problem 28 ==
+==Problem 28==
+The polynomial <math>x^{2n}+1+(x+1)^{2n}</math> is not divisible by <math>x^2+x+1</math> if <math>n</math> equals
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+<math>\text{(A)} \ 17 \qquad
+\text{(B)} \ 20 \qquad
+\text{(C)} \ 21 \qquad
+\text{(D)} \ 64 \qquad
+\text{(E)} \ 65  </math>
+[[1980 AHSME Problems/Problem 28|Solution]]
-[[1980 AHSME Problems/Problem 28|Solution]]
+==Problem 29==
-== Problem 29 ==
+How many ordered triples (x,y,z) of integers satisfy the system of equations below?
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+<cmath>\begin{array}{l} x^2-3xy+2y^2-z^2=31 \\ -x^2+6yz+2z^2=44 \\ x^2+xy+8z^2=100\\ \end{array} </cmath>
+<math>\text{(A)} \ 0 \qquad
+\text{(B)} \ 1 \qquad
+\text{(C)} \ 2 \qquad
+\text{(D)}\ \text{a finite number greater than 2}\qquad
+\text{(E)}\ \text{infinitely many} </math>
 [[1980 AHSME Problems/Problem 29|Solution]]
-== Problem 30 ==
+==Problem 30==
-<math> \textbf{(A) \ }  \qquad \textbf{(B) \ } \qquad \textbf{(C) \ } \qquad \textbf{(D) \ }\qquad \textbf{(E) \ } </math>
+A six digit number (base 10) is squarish if it satisfies the following conditions:
+(i) none of its digits are zero;
+(ii) it is a perfect square; and
+(iii) the first of two digits, the middle two digits and the last two digits of the number are all perfect squares when considered as two digit numbers.
+How many squarish numbers are there?
+<math>\text{(A)} \ 0 \qquad
+\text{(B)} \ 2 \qquad
+\text{(C)} \ 3 \qquad
+\text{(D)} \ 8 \qquad
+\text{(E)} \ 9  </math>
 [[1980 AHSME Problems/Problem 30|Solution]]
 == See also ==
-* [[AHSME]]
-* [[AHSME Problems and Solutions]]
+* [[AMC 12 Problems and Solutions]]
 * [[Mathematics competition resources]]
+{{AHSME box|year=1980|before=[[1979 AHSME]]|after=[[1981 AHSME]]}}
+{{MAA Notice}}