Combinations and permutation

Question 1

Repetition not allowed and order is important (permutation)

Answer 1

n! / (n-r)!

Question 2

Repetition not allowed and combination (order doesn’t matter)

Answer 2

n! / ( r! (n-r)! )

Question 3

repetition allowed and order is imporant

Answer 3

n^r

Question 4

order doesn’t matter and repetition allowed

Answer 4

(n+r-1)! / ( r! (n-1)!)