Question

5. A box contains 2 white, 3 black and 5 red balls. In how many ways can three balls be drawn from the box if at least one black ball is to be included in the draw?​

Answer 1

Answer:

The number of ways of selecting 3 balls out of total 9(2 white, 3 black, 4 red balls) is  

9

C  

3

​  

=  

6

9×8×7

​  

=84

The number of ways of selecting 3 balls out of non-black six balls is  

6

C  

3

​  

=  

3×2×1

6×8×4

​  

=20

The desired number =84−20=64

Explanation: