There are many marbles in a big box. It is known that 30% of the marbles are red, 60% are blue and the remaining 10% is not coloured.

(a) A sample of 5 marbles is picked from the box. Find the probability that this sample contains not more than 2 red marbles.

(b) Given that there are 4 coloured marbles (red or blue) in the sample, find the probability that the majority of the marbles in the sample is red.

I managed to solve (a) but how do you solve (b)???

This is conditional probability isn't it?

Thanks for your help.