What is the smallest positive integer whose factorial ends in exactly two trailing zeros?
10
Trailing zeros are formed by pairs of factors of 2 and 5. In factorials, 5s are rarer than 2s. 5! through 9! include one factor of 5 (5), producing one zero. 10! includes factors of 5 from both 5 and 10, providing two factors of 5 and therefore two trailing zeros.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Medium. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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