Rocco stores his coins in piles of 10 coins each. He has 4 piles of quarters, 6 piles of dimes, 9 piles of nickels, and 5 piles of pennies. How much money does Rocco have?
Stream of thoughts:
21
Each pile has 10 coins, so he has:.

10 * 4 * $.

25 = $10.

00 worth of quarters,.

10 * 6 * $.

10 = $6.

00 worth of dimes,.

10 * 9 * $.

05 = $4.

50 worth of nickels, and.

10 * 5 * $.

01 = $0.

50 worth of pennies.

Altogether he has $10.

00 + $6.

00 + $4.

50 + $0.

50 = $21.

00.

.

Therefore, the answer is 21