SOLUTION: Suppose Tom has 21 coins totaling $4.05. If he has only dimes and quarters, how many of each type does he have?

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Question 1021796: Suppose Tom has 21 coins totaling $4.05. If he has only dimes and quarters, how many of each type does he have?
Answer by MathLover1(20850) About Me  (Show Source):
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let quarters be q and dimes d
if Tom has 21 coins, than
q%2Bd=21............eq.1
if totaling $4.05, than
0.25q%2B0.10d=4.05.........eq.2
start with
q%2Bd=21............eq.1 and solve for q
q=21-d
substitute in eq.2
0.25%2821-d%29%2B0.10d=4.05.........eq.2,solve for d
5.25-0.25d%2B0.10d=4.05
5.25-0.15d=4.05
5.25-4.05=0.15d
1.20=0.15d
d=1.20%2F0.15
d=120%2F15
highlight%28d=8%29
go to
q=21-d substitute 8 for d
q=21-8
highlight%28q=13%29
so, Tom has highlight%2813%29 quarters and highlight%288%29 dimes