Permutations and Combinations

Question 1

Permutations of n things taken r at a time

Answer 1

P(n,r) = n! / (n-r)!

Question 2

Permutations of n things in which q are alike, r are alike, and so on

Answer 2

P = n! / (q!r!……)

Question 3

Permutations of n different things in a circle

Answer 3

P = (n-1)!

Question 4

Combination of n things taken r at a time

Answer 4

C (n,r) = n! / (n-r)!r!

Question 5

Combination of n different things 1, 2, 3, …n at a time

Answer 5

C = 2^n - 1