The Sciences

Fuzzy Math: Dubious Change

Buying a pack of gum can leave you $5 richer.

By Alex StoneMay 16, 2007 5:00 AM

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A con man walks into a store and buys a pack of gum that costs 75 cents with a $5 bill, and the cashier hands him back $4.25. Before the register closes, the grifter offers the cashier five singles in exchange for his fiver back. When the cashier agrees, the con man slips him four ones and a fiver instead of five singles, while taking back his original $5 bill. When the cashier alerts him to the mistake, the schemer feigns surprise and says, “I’ll add one more dollar to make an even 10, and give me back a 10 spot.” The cashier agrees, and the rogue walks out five bucks richer. “Shortchanging” is an old scam. The trick is that when the con artist takes back his original five and gives the cashier nine, the store now has five of its dollars and four of the customer’s. When the swindler adds one more dollar, he should only get back 5, but the confused cashier gives him 10 in return.

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