An old man is selling watermelon. His pricelist says 1 for 3 dollars and 3 for 10 dollars.

A young man stop by and asked to buy a watermelon.

"That will be 3 dollars" says the old man.

Then the young man buy another one and another one, paying 3 dollars for each time.

As the young man was walking away, he turns around, grins and said "Hey old man, do you realized that I have just bought 3 watermelon for only 9 dollars? Maybe business is not your thing!"

The old man smiles and mumbles to himself "People are funny. Everytime they buy 3 watermelons instead of 1, yet they keep trying to teach me how to do business."