In the days when an ice cream cost much less, a 10 year old girl entered a coffee shop and sat at a table. A waitress put a glass of water in front of her.
“How much is an ice cream” ?

“50 cents,” replied the waitress.

The little girl pulled her hand out of her pocket and studied a number of coins in it.

“How much is a dish of plain ice cream?” she inquired. Some people were now waiting for a table and the waitress was a rather impatient.

“35 cents,” she said brusquely.

The little girl again counted the coins. “I’ll have the plain ice cream,” she said. The waitress brought the ice cream, put the bill on the table and walked away. The girl finished the ice cream, paid the cashier and departed. When the waitress came back, she began wiping down the table and then swallowed hard at what she saw.

There, placed neatly beside the empty dish, were 15 cents – her tip.