For which value of n ∈ N ,   n ! has 13 trailing zeros?

For which value of nN, n! has 13 trailing zeros?
  1. 51
  2. 54
  3. 57
  4. 60

Solution

We know in n! exponent of 5 is always less than or equal to exponent of 2

Hence, exponent of 5 is equal to the number of trailing zeroes

We know, exponent of 5 in n! is given as 

13=n5+n52+n53+...

Using n=57 from the options, we get 

=575+5725+57125

=11+2+0 ...

So, in 57! the power of 5 is 13

Asked in: AP EAMCET 2020 (23 Sep Shift 1)

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