A record store put 30 old rock CDs on sale two-for-a-dollar, and 30 pop CDs on sale three-for-a-dollar. All 60 sold in a single day. The rock CDs brought in $15, and the pop CDs brought in $10 -- totalling $25.

The next day, there were another 30 of each to sell. "Why bother sorting them into piles?" asked the clerk to himself. "All 30 rock CDs sold at 2-for-a-dollar, and all 30 pop CDs at 3-for-a-dollar, so I'll just sell them all at 5 for $2."

Sure enough, all the CDs sold. But when he checked his profits, he had only made $24.

Where's the last dollar?

 

 

 

 

 

(Based on The Missing Dollar from aha! Gotcha (1982), Martin Gardener.)

Copyright © 2009 Elaine Simmt