Given White ball = 5
Red ball = 7
Black ball = 8
Total number of balls = 5 + 7 + 8 = 20
∴ Probability of getting first white ball
= 5C1/20C1 = 5/20 [∵ nC1 = n]
= 1/4
Probability of getting second white ball
= 4C1/19C1 = 4/19
Probability of getting third white ball
= 3C1/18C1 = 3/18 = 1/6
Probability of getting fourth white ball
= 2C1/17C1 = 2/17
Probability of getting all white balls
= 1/4 x 4/19 x 1/6 x 2/17 = 1/969
