Question 881285
If all the coins were nickels, 500 coins would be $25.00 (500*5)
The value is 30.00, so the difference is $5.00
The difference between a dime and a nickel is .05
Divide 5.00 by .05 to get 100
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100 of the coins are dimes (100 * .10 = $10.00)
The remainder (400) is nickels (400 * .05 = $20.00)
$20 + $10 = $30
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There are many ways to approach this sort of problem.  For me, "visual" is easiest.