Multiple choice general knowledge math & puzzles

find smalest value of n such that n! contains 31 zeroes

  1. 120

  2. 125

  3. 130

  4. 135
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Trailing zeros in n! come from factors of 10 = 2×5. Since there are always more factors of 2 than 5, we count factors of 5. For n=125: floor(125/5)=25, floor(125/25)=5, floor(125/125)=1. Total = 25+5+1=31 zeros. For n=120: floor(120/5)=24, floor(120/25)=4 → 28 zeros. So 125 is the smallest.

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