Mock AIME II 2012 Problems

Problem 1

Given that $\left(\dfrac{6^2-1}{6^2+11}\right)\left(\dfrac{7^2-2}{7^2+12}\right)\left(\dfrac{8^2-3}{8^2+13}\right)\cdots\left(\dfrac{2012^2-2007}{2012^2+2017}\right)=\dfrac{m}{n},$ where $m$ and $n$ are positive relatively prime integers, find the remainder when $m+n$ is divided by $1000$ .

Solution

Problem 2

Let $\{a_n\}$ be a recursion defined such that $a_1=1, a_2=20$ , and $a_n=\sqrt{\left| a_{n-1}^2-a_{n-2}^2 \right|}$ where $n\ge 3$ , and $n$ is an integer. If $a_m=k$ for $k$ being a positive integer greater than $1$ and $m$ being a positive integer greater than 2, find the smallest possible value of $m+k$ .

Solution

Problem 3

The $\textit{digital root}$ of a number is defined as the result obtained by repeatedly adding the digits of the number until a single digit remains. For example, the $\textit{digital root}$ of $237$ is $3$ $(2+3+7=12$ , $1+2=3)$ . Find the $\textit{digital root}$ of $2012^{2012^{2012}}$ .

Solution

Problem 4

Let $\triangle ABC$ be a triangle, and let $I_A$ , $I_B$ , and $I_C$ be the points where the angle bisectors of $A$ , $B$ , and $C$ , respectfully, intersect the sides opposite them. Given that $AI_B=5$ , $CI_B=4$ , and $CI_A=3$ , then the ratio $AI_C:BI_C$ can be written in the form $\frac{m}{n}$ where $m$ and $n$ are positive relatively prime integers. Find $m+n$ .

Solution

Problem 5

A fair die with $12$ sides numbered $1$ through $12$ inclusive is rolled $n$ times. The probability that the sum of the rolls is $2012$ is nonzero and is equivalent to the probability that a sum of $k$ is rolled. Find the minimum value of $k$ .

Solution

Problem 6

A circle with radius $5$ and center in the first quadrant is placed so that it is tangent to the $y$ -axis. If the line passing through the origin that is tangent to the circle has slope $\dfrac{1}{2}$ , then the $y$ -coordinate of the center of the circle can be written in the form $\dfrac{m+\sqrt{n}}{p}$ where $m$ , $n$ , and $p$ are positive integers, and $m$ and $p$ are relatively prime. Find $m+n+p$ .

Solution

Problem 7

Given $x, y$ are positive real numbers that satisfy $3x+4y+1=3\sqrt{x}+2\sqrt{y}$ , then the value $xy$ can be expressed as $\frac{m}{n}$ , where $m$ and $n$ are relatively prime positive integers. Find $m+n$ . Solution

Problem 8

Let $A$ be a point outside circle $\Omega$ with center $O$ and radius $9$ such that the tangents from $A$ to $\Omega$ , $AB$ and $AC$ , form $\angle BAO=15^{\circ}$ . Let $AO$ first intersect the circle at $D$ , and extend the parallel to $AB$ from $D$ to meet the circle at $E$ . The length $EC^2=m+k\sqrt{n}$ , where $m$ , $n$ , and $k$ are positive integers and $n$ is not divisible by the square of any prime. Find $m+n+k$ .

Solution

Problem 9

In $\triangle ABC$ , $AB=12$ , $AC=20$ , and $\angle ABC=120^\circ$ . $D, E,$ and $F$ lie on $\overline{AC}, \overline{AB}$ , and $\overline{BC}$ , respectively. If $AE=\frac{1}{4}AB, BF=\frac{1}{4}BC$ , and $AD=\frac{1}{4}AC$ , the area of $\triangle DEF$ can be expressed in the form $\frac{a\sqrt{b}-c\sqrt{d}}{e}$ where $a, b, c, d, e$ are all positive integers, and $b$ and $d$ do not have any perfect squares greater than $1$ as divisors. Find $a+b+c+d+e$ .

Solution

Problem 10

Call a set of positive integers $\mathcal{S}$ $\textit{lucky}$ if it can be split into two nonempty disjoint subsets $\mathcal{A}$ and $\mathcal{B}$ with $A\cup B=S$ such that the product of the elements in $\mathcal{A}$ and the product of the elements in $\mathcal{B}$ sum up to the cardinality of $\mathcal{S}$ . Find the number of $\textit{lucky}$ sets such that the largest element is less than $15$ . (Disjoint subsets have no elements in common, and the cardinality of a set is the number of elements in the set.)

Solution

Problem 11

There exist real values of $a$ and $b$ such that $a+b=n$ , $a^2+b^2=2n$ , and $a^3+b^3=3n$ for some value of $n$ . Let $S$ be the sum of all possible values of $a^4+b^4$ . Find $S$ .

Solution

Problem 12

Let $\log_{a}b=5\log_{b}ac^4=3\log_{c}a^2b$ . Assume the value of $\log_ab$ has three real solutions $x,y,z$ . If $\frac{1}{x}+\frac{1}{y}+\frac{1}{z}=-\frac{m}{n}$ , where $m$ and $n$ are relatively prime positive integers, find $m+n$ .

Solution

Problem 13

Regular octahedron $ABCDEF$ (such that points $B$ , $C$ , $D$ , and $E$ are coplanar and form the vertices of a square) is divided along plane $\mathcal{P}$ , parallel to line $BC$ , into two polyhedra of equal volume. The cosine of the acute angle plane $\mathcal{P}$ makes with plane $BCDE$ is $\frac{1}{3}$ . Given that $AB=30$ , find the area of the cross section made by plane $\mathcal{P}$ with octahedron $ABCDEF$ .

Solution

Problem 14

Call a number a $\textit{near Carmichael number}$ if for all prime divisors $p$ of the $\textit{near Carmichael number}$ , $n$ , $(p-1)$ divides $(n-1)$ and $n$ is not prime. Find the sum of all two digit $\textit{near Carmichael numbers}$ .

Solution

Problem 15

Define $a_n=\sum_{i=0}^{n}f(i)$ for $n\ge 0$ and $a_n=0$ . Given that $f(x)$ is a polynomial, and $a_1, a_2+1, a_3+8, a_4+27, a_5+64, a_6+125, \cdots$ is an arithmetic sequence, find the smallest positive integer value of $x$ such that $f(x)<-2012$ .