DAY 447

THREE COINS

Credit: NPR Weekend Edition Sunday Puzzle
July 3, 2005
Presented by Will Shortz
Puzzle by Eric Friedman

[Note from JA: I do not know how this problem was solved, as no explanation was given. This puzzle was used in the U.S. Puzzle Championship in 2005. There are two possible answers.]

A certain country mints coins in only three denominations. Each denomination is an integral number (1, 3, 4, etc.) The amounts 20, 23, and 29 can be made exactly by using three coins. What are the denominations of the coins?

Answers:

6, 7, 11 or
5, 9, 10