SOLUTION: A box containing nickels, dimes, and quarters is worth a total of $2.10. There are twice as many dimes as quarters, and the number of nickels is two less than the number of dimes.

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Question 862728: A box containing nickels, dimes, and quarters is worth a total of $2.10. There are twice as many dimes as quarters, and the number of nickels is two less than the number of dimes. How many of each coin are there?
Answer by ben720(159) About Me  (Show Source):
You can put this solution on YOUR website!
Quarters * 25cents + Dimes * 10cents + Nickels * 5cents = $2.10
0.25Q+0.1D+0.05N=2.1

Let D = number of dimes
Let quarters = D/2 "There are twice as many dimes as quarters"
Let nickels = D-2 "...the number of nickels is two less than the number of dimes."

0.25%28d%2F2%29%2B0.1d%2B0.05%28d-2%29=2.1
Distribute
d%2F8%2Bd%2F10%2Bd%2F20-1%2F10=2.1
Add 1/10 to both sides.
d%2F8%2Bd%2F10%2Bd%2F20=2.2
Convert the fractions to 80ths.
10d%2F80%2B8d%2F80%2B4d%2F80=2.2
Add the fractions
22d%2F80=2.2
Multiply both sides by 80%2F22
d=8
There are 8 dimes, 4 quarters, and 6 nickels.