SOLUTION: mary has 54 coins which are either 20-cent coins or 50-cent coins.If the total amount is $20.70, how many 20-cent coins does Mary have?

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Question 718117: mary has 54 coins which are either 20-cent coins or 50-cent coins.If the total amount is $20.70, how many 20-cent coins does Mary have?
Answer by checkley79(3341) About Me  (Show Source):
You can put this solution on YOUR website!
X+Y=54
X=54-Y
.20X+.50Y=20.70
.20(54-Y)+.50Y=20.70
10.80-.20Y+.50Y=20.70
.30Y=20.70-10.80
.30Y=9.90
Y=9.90/.30
Y=33 50-CENT COINS.
X+33=54
X=54-33
X=21 20-CENT COINS.
PROOF:
.20*21+.50*33=20.70
4.20+16.50=20-70
20.70=20.70