Question 171421
Joe has a collection of nickels and dimes that is worth $5.65. If the number of dimes are doubled and the number of nickels were increased by 8, the value of the coins would be $10.45. How many dimes does he have?
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Value equation:   5n + 10d = 565 cents
value equation:5(n+8)+10(2d)=1045 cents
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Rearrange: 
5n  +  10d  = 565
5n  +  20d  = 1005
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10d = 440
d = 44 (# of dimes)
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Substitute to solve for "n":
5n + 440 = 565
5n = 125
n =25 (# of nickels) 
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Cheers,
Stan H.