9
$\begingroup$

Possible Duplicate:
How come the number $N!$ can terminate in exactly $1,2,3,4,$ or $6$ zeroes but never $5$ zeroes?

The number of zeros which are not possible at the end of the $n!$ is:

$a) 82 \quad\quad\quad b) 73 \quad\quad\quad c) 156 \quad\quad\quad d) \text{ none of these }$

I was trying to solve this problem. I know how to calculate the no of zeros in factorial but have no idea how to work out this problem quickly.

  • 0
    Is there something that precludes you from simply computing the first few hundred factorials on a computer, then inspecting their digits?2011-01-20
  • 0
    Yes. This question belongs to a quantitative aptitude section of CAT(Common aptitude test) which must be answered in least possible time(varying from 1 to 3 mins)2011-01-20
  • 0
    This recent question is related: http://math.stackexchange.com/q/17916/1242.2011-01-20
  • 1
    So this is not really homework... btw, @user5918, you seem to posting a lot of questions without actually showing any of your working. It is considered to be in bad form to do that. Please put some thought/effort into your questions before asking them here.2011-01-20

2 Answers 2