Question

You want to borrow three rock CDs from your friend. She loves math puzzles and she always makes you solve one before you can borrow her stuff. Here’s the puzzle: Before you borrow three CDs, she will have 39 CDs. She will have half as many country CDs as rock CDs, and one-fourth as many soundtracks as country CDs. How many of each type of CD does she have after you borrow three rock CDs?

Answer 1

interesting puzzle,

total CDs=$39$

country CDs $c$ is half of rock CDs $r$, $r=2c$

and one fourth of soundtrack $s$ as country CDs , $c=4s$

express in common variable s, $r+c+s=39$

$2(4s)+4s+s=39 \implies s=3$

so $c=12$ and $r=24$

after borrowing 3 rock CDs, there be $21$ rock CDs rest will be same