1. ## premutation

Evaluate P(7,3)

what does the p stand for and how do i solve it? the question before it was evaluate 6! (720) so it might be along those lines but is this a typo?

2. Originally Posted by andy11
Evaluate P(7,3)

what does the p stand for and how do i solve it? the question before it was evaluate 6! (720) so it might be along those lines but is this a typo?
Judging by what your previous question asked, i think you want the permutation

$\displaystyle P(n,r) = \frac {n!}{(n - r)!}$

So, $\displaystyle P(7,3) = \frac {7!}{(7 - 3)!} = \frac {7!}{4!} = 7(6)(5) = 210$

For the record, you may encounter these other notations in the future, so i'll tell them to you.

$\displaystyle P(n,r) = _n P _r = P_{r}^{n}$

3. P could stand for permutation: $\displaystyle P(n,j) = \frac{{n!}}{{(n - j)!}} = n\left( {n - 1} \right)\left( {n - 2} \right) \cdots \left( {n - j + 1} \right)$

4. oh ok yeah thats the nCr key right?

5. Originally Posted by andy11
oh ok yeah thats the nCr key right?
no, there is an nPr key. nCr is something different, it's what we call a "combination"

6. ok yeah i know what you mean now.. thanks