Permutations and Combinations!

Permutation: when the order is important or different.
nPr=n!/(n-r)!

Combination: when the order is not important or identical.
nCr=n!/(n-r)!r!

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Ex.1: How many ways can a club choose 3 offices; a president, a vice-president and a secretary, if there are 10 members?:

Since the order is important you would use Permutation

10P3=720 ways.

Ex.2: How many ways can 6 books be given to 6 friends if they are all identical?:

Since the books are identical you would use Combination

6C6=1 way.