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1974 AMC 12

Question 1

If $x\ne0$ or $4$ and $y\ne0$ or $6,$ then $\frac2x+\frac3y=\frac12$ is equivalent to
  1. $4x+3y=xy$
  2. $y=\frac{4x}{6-y}$
  3. $\frac{x}{2}+\frac{y}{3}=2$
  4. $\frac{4y}{y-6}=x$
  5. none of these

Question 2

Let $x_1$ and $x_2$ be such that $x_1\ne x_2$ and $3x_i^2-hx_i=b,$ $i=1,$ $2.$ Then $x_1+x_2$ equals
  1. $-\frac h3$
  2. $\frac h3$
  3. $\frac b3$
  4. $2b$
  5. $-\frac b3$

Question 3

The coefficient of $x^7$ in the polynomial expansion of $$
(1+2x-x^2)^4
$$ is
  1. $-8$
  2. $12$
  3. $6$
  4. $-12$
  5. none of these

Question 4

What is the remainder when $x^{51}+51$ is divided by $x+1?$
  1. $0$
  2. $1$
  3. $49$
  4. $50$
  5. $51$

Question 5

Given a quadrilateral $ABCD$ inscribed in a circle with side $AB$ extended beyond $B$ to point $E,$ if $\angle BAD=92^\circ$ and $\angle ADC=68^\circ,$ find $\angle EBC.$
  1. $66^\circ$
  2. $68^\circ$
  3. $70^\circ$
  4. $88^\circ$
  5. $92^\circ$

Question 6

For positive real numbers $x$ and $y$ define $x*y=\frac{x\cdot y}{x+y};$ then
  1. “$*$” is commutative but not associative
  2. “$*$” is associative but not commutative
  3. “$*$” is neither commutative nor associative
  4. “$*$” is commutative and associative
  5. none of these

Question 7

A town’s population increased by $1{,}200$ people, and then this new population decreased by $11\%.$ The town now had $32$ less people than it did before the $1{,}200$ increase. What is the original population?
  1. $1{,}200$
  2. $11{,}200$
  3. $9{,}968$
  4. $10{,}000$
  5. none of these

Question 8

What is the smallest prime number dividing the sum $3^{11}+5^{13}?$
  1. $2$
  2. $3$
  3. $5$
  4. $3^{11}+5^{13}$
  5. none of these

Question 9

The integers greater than one are arranged in five columns as follows:

$2$ $3$ $4$ $5$ $9$ $8$ $7$ $6$ $10$ $11$ $12$ $13$ $17$ $16$ $15$ $14$ $\vdots$ $\vdots$ $\vdots$ $\vdots$

(Four consecutive integers appear in each row; in the first, third and other odd numbered rows, the integers appear in the last four columns and increase from left to right; in the second, fourth and other even numbered rows, the integers appear in the first four columns and increase from right to left.)

In which column will the number $1{,}000$ fall?
  1. first
  2. second
  3. third
  4. fourth
  5. fifth

Question 10

What is the smallest integral value of $k$ such that $$
2x(kx-4)-x^2+6=0
$$ has no real roots?
  1. $-1$
  2. $2$
  3. $3$
  4. $4$
  5. $5$

Question 11

If $(a,b)$ and $(c,d)$ are two points on the line whose equation is $y=mx+k,$ then the distance between $(a,b)$ and $(c,d),$ in terms of $a,$ $c,$ and $m,$ is
  1. $|a-c|\sqrt{1+m^2}$
  2. $|a+c|\sqrt{1+m^2}$
  3. $\frac{|a-c|}{\sqrt{1+m^2}}$
  4. $|a-c|(1+m^2)$
  5. $|a-c||m|$

Question 12

If $g(x)=1-x^2$ and $f(g(x))=\frac{1-x^2}{x^2}$ when $x\ne0,$ then $f(\frac{1}{2})$ equals
  1. $\frac{3}{4}$
  2. $1$
  3. $3$
  4. $\frac{\sqrt2}{2}$
  5. $\sqrt2$

Question 13

Which of the following is equivalent to “If $P$ is true then $Q$ is false”?
  1. “$P$ is true or $Q$ is false.”
  2. “If $Q$ is false then $P$ is true.”
  3. “If $P$ is false then $Q$ is true.”
  4. “If $Q$ is true then $P$ is false.”
  5. “If $Q$ is true then $P$ is true.”

Question 14

Which statement is correct?
  1. If $x\lt0,$ then $x^2\gt x.$
  2. If $x^2\gt0,$ then $x\gt0.$
  3. If $x^2\gt x,$ then $x\gt0.$
  4. If $x^2\gt x,$ then $x\lt0.$
  5. If $x\lt1,$ then $x^2\lt x.$

Question 15

If $x\lt-2$ then $\bigl|1-|1+x|\bigr|$ equals
  1. $2+x$
  2. $-2-x$
  3. $x$
  4. $-x$
  5. $-2$

Question 16

A circle of radius $r$ is inscribed in a right isosceles triangle, and a circle of radius $R$ is circumscribed about the triangle. Then $\frac{R}{r}$ equals
  1. $1+\sqrt2$
  2. $\frac{2+\sqrt2}{2}$
  3. $\frac{\sqrt2-1}{2}$
  4. $\frac{1+\sqrt2}{2}$
  5. $2(2-\sqrt2)$

Question 17

If $i^2=-1,$ then $(1+i)^{20}-(1-i)^{20}$ equals
  1. $-1024$
  2. $-1024i$
  3. $0$
  4. $1024$
  5. $1024i$

Question 18

If $\log_8 3=p$ and $\log_3 5=q,$ then, in terms of $p$ and $q,$ $\log_{10}5$ equals
  1. $pq$
  2. $\frac{3p+q}{5}$
  3. $\frac{1+3pq}{p+q}$
  4. $\frac{3pq}{1+3pq}$
  5. $p^2+q^2$

Question 19

In the adjoining figure $ABCD$ is a square and $CMN$ is an equilateral triangle. If the area of $ABCD$ is one square inch, then the area of $CMN$ in square inches is

Question illustration
  1. $2\sqrt3-3$
  2. $1-\frac{\sqrt3}{3}$
  3. $\frac{\sqrt3}{4}$
  4. $\frac{\sqrt2}{3}$
  5. $4-2\sqrt3$

Question 20

Let $$
\begin{aligned} T={}&\frac1{3-\sqrt8} -\frac1{\sqrt8-\sqrt7}\\ &+\frac1{\sqrt7-\sqrt6} -\frac1{\sqrt6-\sqrt5}\\ &+\frac1{\sqrt5-2}; \end{aligned}
$$ then
  1. $T\lt1$
  2. $T=1$
  3. $1\lt T\lt2$
  4. $T\gt2$
  5. $\displaystyle
    T=\frac1{\substack{(3-\sqrt8)(\sqrt8-\sqrt7)(\sqrt7-\sqrt6)\\
    {}\cdot(\sqrt6-\sqrt5)(\sqrt5-2)}}$