Permutations and Combinations

If an event can occur in m different ways, following which another event can occur in n different ways, then the total number of occurrence of the eve

If an event can occur in m different ways, following which another event can occur in n different ways, following which a third event can occur in p d

^nP_r = n(n-1)(n-2)...(n-r+1)

^nP_r = n!/(n-r)!

^nP_r = ^nC_r × r!

n! = n(n-1)!

0! = 1

n^r

n!/p!

n!/(p1! p2! ... pk!)

n! = 1 × 2 × 3 × ... × n

n! = n(n-1)!