100 factorial here's  a new problem you might find fun.  the question is:  how many zeroes appear at the end of the rather large number 100! that's 100 factorial, not yelling the number 100. :) I recently used your site for studying for a msft interview.  Although I didn't get any questions from your site that I hadn't already heard before, it did help to see so many logic problems.  thanks!  oh, i got the job by the way. :) Jesse Hersch Friday, March 22, 2002 and if you find that one too easy, why not find how many zero digits *total* are in 100! Jesse Hersch Friday, March 22, 2002 sorry for being redundant.  i just found that this question is already on the site!  oops.  http://www.techinterview.org/Puzzles/fog0000000149.html Jesse Hersch Friday, March 22, 2002 I think the answer to the trailing 0s problem should be 21. for      for    for 10s    5s    100 ------------------- 10  + 10 +  1 why additional 3 ?? I couldn't understand? because I think any even number not ending with 0 if multiplied with 5 gives some number ending with 0. If multiplied by 5 again the number of trailing 0s wont increase. may be my whole understanding of the problem itself is wrong. comments ... Govind Jajoo Friday, March 22, 2002 I take back my posting. I got it now. thanks for ur patience. Govind Jajoo Friday, March 22, 2002   Fog Creek Home