SOLUTION: American Economic History can be purchased as a three-volume set for $88 or each volume can be purchased separately for $39. An economics class spent $1641 for 51 volumes. How many

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Question 718068: American Economic History can be purchased as a three-volume set for $88 or each volume can be purchased separately for $39. An economics class spent $1641 for 51 volumes. How many three-volume sets were ordered?
Answer by checkley79(3341) About Me  (Show Source):
You can put this solution on YOUR website!
X+Y=51
X=51-Y
39X+(88/3)Y=1641
39(51-Y)+29.33Y=1641
1989-39Y+29.33Y=1641
-9.67Y=1641-1989
-9.67Y=-348
Y=-348/-9.67
Y=36 3 VOLUME SETS WERE BOUGHT.
X+36=51
X=51-36
X=15 SINGLE VOLUME WERE BOUGHT.
PROOF:
39*15+(88/3)36=1641
585+88*12=1541
585+1056=1541
1641=1641