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A coin bank has only dimes and quarters. The number of quarters is 1 more than 3 times the number of dimes.
The total value is $6.20. Find the number of dimes
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Let d be the number of dimes.
Then
10d + 25(3d+1) = 620, or
10d + 75d + 25 = 620, or
85d = 620 - 25, 85d = 595, d = = 7.
Answer. 7 dimes.