Question 250751
There is 12.80$ in a vending machine, composed of dimes, nickels and quarters. The amount of dimes is 5 times the amount of nickels. 
The amount of quarters is the amount of nickels plus 15. 
How many of each coin are there ?

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Equations:
Value Equation: 5n + 10d + 25q = 1280 cents
Quantity Eq::::: d = 5n
Quantity Eq::::: q = n+15
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Substitute for d and for n; then solve for "n":
5n + 10(5n) + 25(n+15) = 1280
55n + 25n + 375 = 1280
80n = 905
n = (not a whole number)
Check the posting of your problem.
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Cheers,
Stan H.