Dolly is a college student who works as a part-time server in a restaurant. Her usual tip is 20% of the price of the meal. A customer ordered a piece of pie and said that he would appreciate prompt service. Dolly fulfilled the customer’s request. The customer’s bill was $8, but the customer left a $100 bill on the table and did not ask for a receipt. Dolly gave the cashier $8 and pocketed the $100 bill.
Dolly concludes that the customer thought that he had left a $10 bill, although the customer did not return to correct the apparent mistake. The customer had commented about how much he appreciated Dolly’s prompt service. Dolly thinks that a $2 tip would be sufficient and that the other $98 is like “found money.” How much should Dolly include in her gross income?