Probability

Question

Suppose that a bag contains 8 blue cubes and 4 green cubes. We draw 2 cubes from the bag without replacement. It is given that blue balls are of weight 1Kg and green balls are of weight 0.5 Kg. Suppose that the probability that a given cube in the bag is the next one selected is its weight divided by the sum of the weights of all cubes currently in the bag. What is the probability that both cubes are blue.

Answer 1

4/5 *7/9 = 28/45
as first one is blue remaining blues are 7 so p(b1*b2) = p(b1)*p(b2/b1) (given p(b1) = 4/5 after calculate sum of weights.)