Seven numbers belong together in a well-known group that no other numbers are a part of. Six of them are shown here in encrypted form:
9, 22, 24, 12, ?, 4, 13
What does the question mark stand for?
In Roman numerals, the numbers 1, 5, 10, 50, 100, 500 and 1,000 are represented by the letters I, V, X, L, C, D and M, which have the positions 9, 22, 24, 12, 3, 4 and 13 in the alphabet. The question mark therefore stands for 3.
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This puzzle originally appeared in Spektrum der Wissenschaft and was reproduced with permission.