Question

a box contains 2 white and 3 blue balls.two balls are picked at random,one after the other without replacement.what is the probof picking two balls of different colours?
There are two cases: WB and BW

P(WB)=(2/5)*(3/4)=3/10
P(BW)=(3/5)*(2/4)=3/10
Probability of choosing balls of different colours = 6/10=3/5.

Check:
For same colours
P(WW)=(2/5)*(1/4)=1/10
P(BB)=(3/5)*(2/5)=3/1

P(all)=10/10 OK.

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