what is permutation and combination?

Question

what is multiplication rule and how to use it?

Answer 1

Permutation is basic

nPr=nPr/r!= n!/(n-r)!
ex:8P3
8*7*6*5*4*3*2*1/(8-3)!=8*7*6*5*4*3*2*1/5*4*3*2*1 which equals 336

say you have 5!
that would equal 5*4*3*2*1=120
if you have 5P3 that means stop at three factorials
this means 5*4*3=60
another example 8P5
8*7*6*5*4=6720

the Combination formula is nCr which is equal to nPr/r!
or
n!/(n-r)!*r!
ex:6C2
6*5*4*3*2*1/(6-2)!*2*1
6*5*4*3*2*1/4*3*2*1*2*1
since u have like factors u can cancel out 4*3*2*1 in the numerator and denominator leaving
6*5/2*1 which equals 15

OR you can simply enter it in on your handy TI graphing calculator (if you own one and if you dont buy it!) :-)