Khan Academy: Counting, Permutation and Combination

Question 1

what is the difference between permutation and combination?

Answer 1

A permutation is an act of arranging objects or numbers in order. Combinations are the way of selecting objects or numbers from a group of objects or collections, in such a way that the order of the objects does not matter.

Question 2

what does nPk equal to?

Answer 2

n!/(n-k)!

Question 3

what does nCk equal to?

Answer 3

n!/((n-k)! * k!)

Question 4

Unit test

Answer 4

Ref