Question

When to use permutation and when to use combination?

Answer 1

Permutation -nPr—n!/(n-r)!
Combination—nCr—n!/(n-r)!r!

Answer 2

Permutations are for lists (order matters) andcombinations are for groups (order doesn't matter). A joke: A "combination lock" should really be called a "permutation lock". The order you put the numbers in matters. (A true "combination lock" would accept both 10-17-23 and 23-17-10 as correct.)