Consider the question. Penny has $20. Penny buys 4 pairs of socks for $2 a pair and a hat for $7. How much money does Penny have left?
 If the answer is '5'; explain the reasoning:
Penny buys 4 pairs of socks for $2 x 4 = $8. In total, Penny spent $8 + $7 = $15 on 4 pairs of socks and a hat. Penny has $20 - $15 = $5 left after buying 4 pairs of socks and a hat.