(i) Total number of balls
= 5 + 7 + 8 = 20
Number of white balls = 5
Probability of getting white ball is one chance = 5/20 = 1/4
∵ All events are independent
∴ Required probability = 1/4 × 1/4 × 1/4 × 1/4 = (1/4)4
(ii) Probability of drawing white ball first time
= 3C1 ×1/4 × 1/4 × 1/4
= 3 ×(1/4)3
(iii) P(no ball is white)
∴ Number of other balls = 7 + 8 = 15
∴ Probability of drawing one other colour ball = 15/20 = 3/4
∴ Probability of other colour balls drawn successively (none is white)
= 3/4 × 3/4 × 3/4 × 3/4
= (3/4)4
(iv) P(at least 3 white) = P (four white) + P(three white)
= (1/4)4 + 3/43 = 1/44 = 3/43
= 13/44