Combination?

Question

Solve the following combination. 7C5

1) 15

2) 840

3) 196

4) 21

Answer 1

The formula for nCm (read "n choose m") is n! / (m! * (n-m)!).

 

Here we have 7C5 which is 7! / (5! * 2!), or (7x6x5x4x3x2) / (5x4x3x2x2)

 

Cancel out the 5x4x3x2 on top and bottom and we have 7x6/2 which is 21.