The Counterfeit Bill problem (Sobel and Maletsky 1999).
A customer enters a store and purchases a
pair of slippers for $5, paying for the purchase with a $20 bill. The merchant,
unable to make change, asks the grocer next door to change the bill. The
merchant then gives the customer the slippers and $15 change.
customer leaves, the grocer discovers that the $20 bill is counterfeit and
demands that the shoe-store owner make good for it. The shoe-store owner does
so, and by law is obligated to turn the counterfeit bill over to the FBI.
much does the shoe-store owner lose in this transaction?