Question

The positive integers $x$ and $y$ are the two smallest positive integers for which the product of $360$ and $x$ is a square and the product of $360$ and $y$ is a cube. What is the sum of $x$ and $y?$

$80$

$85$

$115$

$165$

$610$

Solution:

For a number to be a perfect square, every exponent in the prime factorization must be even. For it to be a cube, the exponents must be divisible by $3.$

We can factor $360$ to get $360 = 2^3 \cdot 3^2 \cdot 5.$ For $360x$ to be a perfect square and $x$ to be minimized, $x$ must have one factor of $2$ and one factor of $5.$ Therefore, we can let $x = 10.$

For $360y$ to be a cube, $y$ must have one factor of $3$ and two factors of $5.$ Therefore, we can let $y = 75,$ suggesting $x + y = 85.$

Thus, B is the correct answer.

2009 AMC 8 Problem 17

Solution:

Problem 17 in Other Years