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Question bank AMC12 1972

Exam papers

35 questions

Question 1

The lengths in inches of the three sides of each of four triangles $\mathrm{I},$ $\mathrm{II},$ $\mathrm{III},$ and $\mathrm{IV}$ are as follows: $$
\begin{aligned} \mathrm{I}\quad&3,4,5\\ \mathrm{II}\quad&4,7\frac12,8\frac12\\ \mathrm{III}\quad&7,24,25\\ \mathrm{IV}\quad&3\frac12,4\frac12,5\frac12 \end{aligned}
$$ Of these four given triangles, the only right triangles are:
  1. $\mathrm{I}$ and $\mathrm{II}$
  2. $\mathrm{I}$ and $\mathrm{III}$
  3. $\mathrm{I}$ and $\mathrm{IV}$
  4. $\mathrm{I},$ $\mathrm{II},$ and
    $\mathrm{III}$
  5. $\mathrm{I},$ $\mathrm{II},$ and $\mathrm{IV}$

Question 2

If a dealer could get his goods for $8\%$ less while keeping his selling price fixed, his profit, based on cost, would be increased to $(x+10)\%$ from his present profit of $x\%,$ which is:
  1. $12\%$
  2. $15\%$
  3. $30\%$
  4. $50\%$
  5. $75\%$

Question 3

If $x=\dfrac{1-i\sqrt3}{2},$ where $i=\sqrt{-1},$ then $\dfrac{1}{x^2-x}$ is equal to:
  1. $-2$
  2. $-1$
  3. $1+i\sqrt3$
  4. $1$
  5. $2$

Question 4

The number of solutions to $\{1,2\}\subseteq X\subseteq\{1,2,3,4,5\},$ where $X$ is a subset of $\{1,2,3,4,5\},$ is:
  1. $2$
  2. $4$
  3. $6$
  4. $8$
  5. None of these

Question 5

From among $2^{\frac{1}{2}},$ $3^{\frac{1}{3}},$ $8^{\frac{1}{8}},$ $9^{\frac{1}{9}},$ those which have the greatest and the next to the greatest values, in that order, are:
  1. $3^{\frac{1}{3}},$ $2^{\frac{1}{2}}$
  2. $3^{\frac{1}{3}},$ $8^{\frac{1}{8}}$
  3. $3^{\frac{1}{3}},$ $9^{\frac{1}{9}}$
  4. $8^{\frac{1}{8}},$ $9^{\frac{1}{9}}$
  5. None of these

Question 6

If $3^{2x}+9=10(3^x),$ then the value of $x^2+1$ is:
  1. $1$ only
  2. $5$ only
  3. $1$ or $5$
  4. $2$
  5. $10$

Question 7

If $yz:zx:xy=1:2:3,$ then $\dfrac{x}{yz}:\dfrac{y}{zx}$ is equal to:
  1. $3{:}2$
  2. $1{:}2$
  3. $1{:}4$
  4. $2{:}1$
  5. $4{:}1$

Question 8

If $\lvert x-\log y\rvert=x+\log y,$ where $x$ and $\log y$ are real, then:
  1. $x=0$
  2. $y=1$
  3. $x=0$ and $y=1$
  4. $x(y-1)=0$
  5. None of these

Question 9

Ann and Sue bought identical boxes of stationery. Ann used hers to write $1$-sheet letters and Sue used hers to write $3$-sheet letters. Ann used all the envelopes and had $50$ sheets of paper left, while Sue used all of the sheets of paper and had $50$ envelopes left. The number of sheets of paper in each box was:
  1. $150$
  2. $125$
  3. $120$
  4. $100$
  5. $80$

Question 10

For $x$ real, the inequality $1\le\lvert x-2\rvert\le7$ is equivalent to:
  1. $x\le1$ or $x\ge3$
  2. $1\le x\le3$
  3. $-5\le x\le9$
  4. $-5\le x\le1$ or $3\le x\le9$
  5. $-6\le x\le1$ or $3\le x\le10$

Question 11

The value(s) of $y$ for which the following pair of equations $$
\begin{aligned} x^2+y^2-16&=0,\\ x^2-3y+12&=0 \end{aligned}
$$ may have a real common solution, are:
  1. $4$ only
  2. $-7,$ $4$
  3. $0,$ $4$
  4. no $y$
  5. all $y$

Question 12

The number of cubic feet in the volume of a cube is the same as the number of square inches in its surface area. The length of the edge expressed as a number of feet is:
  1. $6$
  2. $864$
  3. $1728$
  4. $6\times1728$
  5. $2304$

Question 13

Inside square $ABCD$ with sides of length $12$ inches, segment $AE$ is drawn, where $E$ is the point on $DC$ which is $5$ inches from $D.$ The perpendicular bisector of $AE$ is drawn and intersects $AE,$ $AD,$ and $BC$ at points $M,$ $P,$ and $Q,$ respectively. The ratio of segment $PM$ to $MQ$ is:

Question illustration
  1. $5{:}12$
  2. $5{:}13$
  3. $5{:}19$
  4. $1{:}4$
  5. $5{:}21$

Question 14

A triangle has angles of $30^\circ$ and $45^\circ.$ If the side opposite the $45^\circ$ angle has length $8,$ then the side opposite the $30^\circ$ angle has length:
  1. $4$
  2. $4\sqrt2$
  3. $4\sqrt3$
  4. $4\sqrt6$
  5. $6$

Question 15

A contractor estimated that one of his two bricklayers would take $9$ hours to build a certain wall and the other $10$ hours. However, he knew from experience that when they worked together, their combined output fell by $10$ bricks per hour. Being in a hurry, he put both men on the job and found that it took exactly $5$ hours to build the wall. The number of bricks in the wall was:
  1. $500$
  2. $550$
  3. $900$
  4. $950$
  5. $960$

Question 16

There are two positive numbers that may be inserted between $3$ and $9$ such that the first three are in geometric progression while the last three are in arithmetic progression. The sum of those two positive numbers is:
  1. $13\frac12$
  2. $11\frac14$
  3. $10\frac12$
  4. $10$
  5. $9\frac12$

Question 17

A piece of string is cut in two at a point selected at random. The probability that the longer piece is at least $x$ times as large as the shorter piece is:
  1. $\dfrac12$
  2. $\dfrac2x$
  3. $\dfrac1{x+1}$
  4. $\dfrac1x$
  5. $\dfrac2{x+1}$

Question 18

Let $ABCD$ be a trapezoid with the measure of base $AB$ twice that of base $DC,$ and let $E$ be the point of intersection of the diagonals. If the measure of diagonal $AC$ is $11,$ then that of segment $EC$ is equal to:
  1. $3\frac23$
  2. $3\frac34$
  3. $4$
  4. $3\frac12$
  5. $3$

Question 19

The sum of the first $n$ terms of the sequence $$
\begin{gathered} 1,\ (1+2),\ (1+2+2^2),\\ \ldots,\ (1+2+2^2+\cdots+2^{n-1}) \end{gathered}
$$ in terms of $n$ is:
  1. $2^n$
  2. $2^n-n$
  3. $2^{n+1}-n$
  4. $2^{n+1}-n-2$
  5. $n\cdot2^n$

Question 20

If $\tan x=\dfrac{2ab}{a^2-b^2},$ where $a\gt b\gt0$ and $0^\circ\lt x\lt90^\circ,$ then $\sin x$ is equal to:
  1. $\dfrac ab$
  2. $\dfrac ba$
  3. $\dfrac{\sqrt{a^2-b^2}}{2a}$
  4. $\dfrac{\sqrt{a^2-b^2}}{2ab}$
  5. $\dfrac{2ab}{a^2+b^2}$