Posted by Mari on Thursday, January 19, 2012 at 9:56pm.
Kate bought 3 CDs and 1 DVD at a store. Her friend Joel bought 2 CDs and 2 DVDs. If Kate spent $20 and Joel spent $22, determine the cost of a CD and DVD.
~Please provide an explanation as well.
Please and thanks!

Math.  Reiny, Thursday, January 19, 2012 at 11:28pm
cost of CD  x
cost of DVD  y
3x + y = 20 > y = 203x
2x + 2y = 22
x +y = 11
use substitution:
x + (203x) = 11
2x = 9
x = 4.5
then y = 6.5