math
posted by Sandy on .
A bag contains 3 red, 5 black and 5 blue marbles. Four marbles are selected at random without replacement:
 the probability that all 4 are black?
the probability that exactly two are blue and none are red?

2/5

First black marble = 5/13, second = 4/12, third = 3/11, fourth = 2/10.
The probability of all events occurring is found by multiplying the individual probabilities.
First blue = 5/13, second = 4/12, first nonred = 8/11, second nonred = 7/10.
The probability of all events occurring is found by multiplying the individual probabilities.