Permutations and combinations

Question 1

0!

Answer 1

1

Question 2

What is n!?

Answer 2

The number of ways of arranging n distinct items

Question 3

What is ⁿP_r?

Answer 3

n!/(n-r)! the number of permutations of r items from n distinct items (order matters!)

Question 4

What is ⁿC_r?

Answer 4

n!/r!(n-r)! the number of combinations of r items from n distinct items (order does not matter!)