1984 AIME Problems

Problem 1

Find the value of $\displaystyle a_2+a_4+a_6+a_8+\ldots+a_{98}$ if $\displaystyle a_1$ , $\displaystyle a_2$ , $\displaystyle a_3\ldots$ is an arithmetic progression with common difference 1, and $\displaystyle a_1+a_2+a_3+\ldots+a_{98}=137$ .

Solution

Problem 2

The integer $\displaystyle n$ is the smallest positive multiple of $\displaystyle 15$ such that every digit of $\displaystyle n$ is either $\displaystyle 8$ or $\displaystyle 0$ . Compute $\frac{n}{15}$ .

Solution

Problem 3

A point $\displaystyle P$ is chosen in the interior of $\displaystyle \triangle ABC$ such that when lines are drawn through $\displaystyle P$ parallel to the sides of $\displaystyle \triangle ABC$ , the resulting smaller triangles $\displaystyle t_{1}$ , $\displaystyle t_{2}$ , and $\displaystyle t_{3}$ in the figure, have areas $\displaystyle 4$ , $\displaystyle 9$ , and $\displaystyle 49$ , respectively. Find the area of $\displaystyle \triangle ABC$ .

Solution

Problem 4

Let $\displaystyle S$ be a list of positive integers - not necessarily distinct - in which the number $\displaystyle 68$ appears. The arithmetic mean of the numbers in $\displaystyle S$ is $\displaystyle 56$ . However, if $\displaystyle 68$ is removed, the arithmetic mean of the numbers is $\displaystyle 55$ . What's the largest number that can appear in $\displaystyle S$ ?

Solution

Problem 5

Determine the value of $ab$ if $\log_8a+\log_4b^2=5$ and $\log_8b+\log_4a^2=7$ .

Solution

Problem 6

Three circles, each of radius $\displaystyle 3$ , are drawn with centers at $\displaystyle (14, 92)$ , $\displaystyle (17, 76)$ , and $\displaystyle (19, 84)$ . A line passing through $\displaystyle (17,76)$ is such that the total area of the parts of the three circles to one side of the line is equal to the total area of the parts of the three circles to the other side of it. What is the absolute value of the slope of this line?

Solution

Problem 7

The function f is defined on the set of integers and satisfies $f(n)= \begin{cases} n-3 & \mbox{if }n\ge 1000 \\ f(f(n+5)) & \mbox{if }n<1000 \end{cases}$

Find $\displaystyle f(84)$ .

Solution

Problem 8

The equation $\displaystyle z^6+z^3+1$ has complex roots with argument $\theta$ between $90^\circ$ and $180^\circ$ in thet complex plane. Determine the degree measure of $\theta$ .

Solution

Problem 9

In tetrahedron $\displaystyle ABCD$ , edge $\displaystyle ABC$ has length 3 cm. The area of face $\displaystyle AMC$ is $\displaystyle 15\mbox{cm}^2$ and the area of face $\displaystyle ABD$ is $\displaystyle 12 \mbox { cm}^2$ . These two faces meet each other at a $30^\circ$ angle. Find the volume of the tetrahedron in $\displaystyle \mbox{cm}^3$ .

Solution

Problem 10

Mary told John her score on the American High School Mathematics Examination (AHSME), which was over $\displaystyle 80$ . From this, John was able to determine the number of problems Mary solved correctly. If Mary's score had been any lower, but still over $\displaystyle 80$ , John could not have determined this. What was Mary's score? (Recall that the AHSME consists of $\displaystyle 30$ multiple choice problems and that one's score, $\displaystyle s$ , is computed by the formula $\displaystyle s=30+4c-w$ , where $\displaystyle c$ is the number of correct answers and $\displaystyle w$ is the number of wrong answers. Students are not penalized for problems left unanswered.)

Solution

Problem 11

A gardener plants three maple trees, four oaks, and five birch trees in a row. He plants them in random order, each arrangement being equally likely. Let $\frac m n$ in lowest terms be the probability that no two birch trees are next to one another. Find $\displaystyle m+n$ .

Solution

Problem 12

A function $\displaystyle f$ is defined for all real numbers and satisfies $\displaystyle f(2+x)=f(2-x)$ and $\displaystyle f(7+x)=f(7-x)$ for all $\displaystyle x$ . If $\displaystyle x=0$ is a root for $\displaystyle f(x)=0$ , what is the least number of roots $\displaystyle f(x)=0$ must have in the interval $\displaystyle -1000\leq x \leq 1000$ ?