Enigma 1350: All but one
1 February 2014
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From New Scientist #2509, 23rd July 2005
Joe asked Penny to think of four different positive digits and add up the 24 different four-digit numbers that could be made using the four digits. Then he asked her to subtract just one of the four-digit numbers from the total and write down the new total. When asked what number she had written down, Penny replied: “122??0.”
Joe didn’t quite hear the fourth or fifth digits. But he was able to work out the number Penny had subtracted.
What was that number?