So the boy is our one day and wants to buy a Coke. He approaches a street vendor and asks how much. The vendor replies, "$2.56."

The boy says, "I'll give you $1.28." The vendor is outraged at first and tries to negotiate a higher price, but fails. He finally gives in, "Okay, $1."

The boy replies, "64 cents." The vendor is outraged but eventually agrees again.

This continues until the price is at 2 cents. The vendor says, "It's pointless now, just have it for free."

The boy says, "I'll take two."