# Math Help - CD's

1. ## CD's

A DJ found a music store that had a great collection of used CD's. he purshased 38 CD's for a total of $235. The purchase included CD's priced at either$5.00 or $8.00. How many CD's in each price category did the DJ buy? 2. Originally Posted by wild_flowr69 A DJ found a music store that had a great collection of used CD's. he purshased 38 CD's for a total of$235. The purchase included CD's priced at either $5.00 or$8.00. How many CD's in each price category did the DJ buy?
Call the number of CDs bought at $5.00 x. Call the number of CDs bought at$8.00 y. We know that the total cost was \$235, so:
$5x+8y=235$.

Additionally, we know that 38 CDs were bought, so:
$x+y=38$.

Two equations, two unknowns, so you can solve for x and y.

-Dan

3. Let me continue from topsquark's solution:
The equations
$\left\{\begin{array}{cc}5x+8y&=235\\x+y&=38\end{ar ray}\right$
In the second equation solve for $y$:
$y=38-x$
Substitute that into the first:
$5x+8(38-x)=235$
Now solve it,
$5x+304-8x=235$
Thus,
$-3x=-69$
Thus,
$x=23$
Thus,
$y=15$