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 $235, so:$\displaystyle 5x+8y=235$. Additionally, we know that 38 CDs were bought, so:$\displaystyle x+y=38$. Two equations, two unknowns, so you can solve for x and y. -Dan 3. Let me continue from topsquark's solution: The equations$\displaystyle \left\{\begin{array}{cc}5x+8y&=235\\x+y&=38\end{ar ray}\right$In the second equation solve for$\displaystyle y$:$\displaystyle y=38-x$Substitute that into the first:$\displaystyle 5x+8(38-x)=235$Now solve it,$\displaystyle 5x+304-8x=235$Thus,$\displaystyle -3x=-69$Thus,$\displaystyle x=23$Thus,$\displaystyle y=15\$