SOLUTION: For moving purposes, the Hendersons bought 25 card board boxes for $97.50. There were two kinds of boxes; the large ones cost $ 7.50 per box, and the small ones cost $3 per box.

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Question 114006: For moving purposes, the Hendersons bought 25 card board boxes for $97.50. There were two kinds of boxes; the large ones cost $ 7.50 per box, and the small ones cost $3 per box. HOw many boxes of each kind did they buy?
Answer by checkley71(8403) About Me  (Show Source):
You can put this solution on YOUR website!
7.50L+3S=97.50
L+S=25 OR L=25-S.
NOW SUBSTITUTE (25-S) FOR L IN THE OTHER EQUATION & SOLVE FOR S.
7.50(25-S)+3S=97.50
187.5-7.5S+3S=97.50
-4.5S=97.50-187.50
-4.5S=-90
S=-90/-4.5
S=20 THE NUMBER OF SMALL BOXES BOUGHT.
25-20=5 LARGE BOXES BOUGHT.
PROOF
7.50*5+3*20=97.5
37.5+60=97.5
97.5=97.5