# The store has CDs for 10 dollars, and 15 dollars. You have 55 dollars. How do you write an equation that represents the different numbers of 10 dollars, and 15 dollar CDs that you can buy?

Nov 17, 2015

You should get: $10 x + 15 y = 55$

#### Explanation:

Call the two types of CDs $x$ and $y$; so you get:
$10 x + 15 y = 55$

For example if you buy $1$ of the first type you get:

$10 \cdot 1 + 15 y = 55$ rearranging:

$15 y = 55 - 10$

$y = \frac{45}{15} = 3$ of the second type.