There are 20 marbles in a bag and 10 of them are blue. What is the probability that any 1 marble drawn at random will not be blue?
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?