Your piggy bank contains $19.75 in dimes and quarters. There are 100 coins in all. How many dimes are there?

If all were quarters, you would have $25. You have $5.25 less than that. Your total amount is decreased from $25 by $0.15 for each dime you have instead of a quarter.   $5.25/$0.15 = 35 You have 35 dimes.

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Check   65*.25 + 35*.10 = 16.25 + 3.50 = 19.75