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Rob has 40 coins, all in dimes and quarters, worth $7.60. How many of each coin does he have?
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Let d = the number of dimes.
Then the number of quarters is (40-d).
The dimes contribute 10d cents to the total.
The quarters contribute 25*(40-d) cents to the total.
The "value" equation is
10d + 25*(40-d) = 760.
Simplify and solve for x:
10d + 1000 - 25d = 760, or
-15d = 1000-660 ---> -15d = -240.
d = = 16.
Answer. 16 dimes and 40-16 = 24 quarters.
