||One teenager goes up to a food booth at a fair and
says, "A cola, please." The man working the booth
asks, "Regular or diet?" The teenager asks, "What's
the difference?" and is told that the regular costs
90 cents but that the diet soda costs $1. The teenager
says, "Give me a diet cola, please" and places a
dollar on the counter.
Next, another teenager comes up to the booth
and says, "A cola, please," placing a dollar on
the counter. The man in the booth gives him a
How did the man in the booth know which soda-regular
or diet-the second teenager wanted?
||The second teenager put a dollar in change on the
counter: 2 quarters and 5 dimes. If the teenager
had wanted a regular cola, he would have put only
2 quarters and 4 dimes on the counter.
Source: Inspired by a puzzle
in Mensa Presents Mighty Mind Boosters, P. Carter,
J. Fulton, and K. Russell. New York: Barnes &