• Advertisement
Sign in to follow this  

factorial question

This topic is 4799 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Can someone show me how to simplify this factorial: (n-1)! / ( (n-i-1)! i! ) which results in to: 1/(n-i) + 1/i

Share this post


Link to post
Share on other sites
Advertisement
1. Is this homework? Forum FAQ
2. Are you sure it reduces to that? I'm not going to work it but that seems to be a mighty peculiar answer.

Share this post


Link to post
Share on other sites
No it's not home work. I'm just looking at a solution to an exam (http://www.dgp.toronto.edu/~hertzman/courses/csc418/winter_2003/final-solutions.pdf), and I don't know how that factorial got reduced to that form. I haven't done factorial stuff in quite a while, so I'm just wondering how it's done.

Share this post


Link to post
Share on other sites
i'd say start by substituting m as n-1 to give
m! / ( (m-i)! i! )

but I think your answer is incorrect as...

substituting n as 6 and i as 2 gives...

(n-1)! / ( (n-i-1)! i! )
(6-1)! / ( (6-2-1)! 2! )
5! / (3!2!)
120 / 12
10

1/(n-i) + 1/i
1/(6-2) + 1/2
1/(4) + 1/2
3/4

Clearly 10 != 3/4
Are you sure thats the right answer?

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement