At a flea market, Joe bought some DVDs and CDs. The CDs sold for $5.00...

Let x be the number of CDs bought and y be the number of DVDs bought.
The total number of products sold was 17:
$x+y=17$ (1)
The total cost of the items was $73.00:
$5x+3y=73$ (2)
Solve for y using (1) to obtain (3):
$y=17-x$ (3)
Substitute (3) to (2) and solve for x:
$5x+3(17-x)=73$
$5x+51-3x=73$
$2x+51=73$
$2x=22$
$x=11$
Solve for y using (3):
$y=17-11$
$y=6$
Joe bought 11 CDs and 6 DVDs