Thread: Combinatorics/Permut/Solv Eqs Involving Factorial Notation.

Hey any help with the following would be much appreciated:


Solve for n where:

P (n,5)=42 * P (n,3)

based on the fact C(n,r)=n!/(n-r)r! , I got:

n!/(n-5)!5!=42* n!/(n-3)!3!

, is this the right step to start? if not, why not? and what would be the proper solution to this problem???

Originally Posted by AGrondin

Solve for n where:
P (n,5)=42 * P (n,3) based on the fact C(n,r)=n!/(n-r)r!?

Problem: ..
You are using combinations to do permutations.

yes I believe so, any suggestions/help to offer?
Thanks

This my point, you are using he wrong formula.

That would leave me with (n-3)(n-4)=42 leaving me with n=10, n=-3 therefore n=10 ?