Each pile has 10 coins, so he has:
10 * 4 * $.25 = $<<10*4*.25=10.00>>10.00 worth of quarters,
10 * 6 * $.10 = $<<10*6*.10=6.00>>6.00 worth of dimes,
10 * 9 * $.05 = $<<10*9*.05=4.50>>4.50 worth of nickels, and
10 * 5 * $.01 = $<<10*5*.01=0.50>>0.50 worth of pennies.
Altogether he has $10.00 + $6.00 + $4.50 + $0.50 = $<<10+6+4.5+0.5=21.00>>21.00
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