Enigma 1670: How mean?
2 December 2011
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From New Scientist #2836, 29th October 2011 [link]
I recently set a class the following puzzle: “Write down four positive whole numbers less than 100 and then write down their average: choose the original numbers so that overall the five numbers written down use each of the digits 1 to 9 exactly once.”
Three Scandinavian lads in the class were successful. Hola came up with 9, 15, 36 and 48, with average 27. Frack was more cunning – his average was not a whole number – it involved a fraction in its simplest form, like 27¾. Dessie was devious, too, and his average, which was lower than Frack’s, was not a whole number – it involved decimals, like 16.25.
What averages did Frack and Dessie write?