Question
In bag A, there are 5 white and 8 red balls, in bag B, 7 white and 6 red balls and in bag C, 6 white and 5 red balls. One ball is taken out at random from each bag. Find the probability that all the three balls are of the same colour.
Solution
Bag A Bag B Bag C
White 5 7 6
Red 8 6 5
P(all three balls of the same colour) = P(all white or all red)
= P(all white) + P(all red)
= P(WWW) + P(RRR)
= P(W) P(W) P(W) + P(R) P(R) P(R)
