Question

Evaluate C(7, 5).

21
42
1,008

Answer 1

21

Explanation:

This is a combination of 7 objects taken 5 at a time

nCr = n! / r! * (n - r)!

7C5 = 7! / (5! (7-5)!)

= 7! /(5! 2!)

= (7*6*5*4*3*2*1)

-----------------------

5*4*3*2*1 * 2*1

Canceling

= 7*6/ (2*1)

= 21