A box contains 10 red marbles, 20 blue marbles and 30 green marbles. 5 marbles are drawn at random. From the box, what is the probability that :
(i) all are blue?
(ii) at least one is green?
Out of 60 marbles, five marbles can be draw in 60C5 ways.
∴ Total number of elementary events =60C5
(i) Out of 20 blue marbles, five blue marbles can be chosen in 20C5 ways.
∴ Favourable number of events =20C5 ways
Hence, the required probability is given by
(ii) P (no green) =Favorable outcomesTotal outcomes=30C560C5
Thus, P (at least one green)=1-P (no green)