Homework Help: Math.

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 = 20-3x

2x + 2y = 22
x +y = 11
use substitution:
x + (20-3x) = 11
-2x = -9
x = 4.5
then y = 6.5

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