Question

Assume that we have a box containing 7 blue balls and 9 red balls.Assume that we pick 2 balls. What is the probability that both balls are blue?

Answer 1

7/16 * 6/15

Answer 2

Assume that we have a box containing 7 blue balls and 9 red balls. Assume that we pick (and remove) 2 balls. Then we pick one extra ball later. What is the probability that the third ball is blue knowing that the previous two balls were both red?

Answer 3

If both of the first two ball are red, that means now, before picking the third ball, you have 7 blue balls and 7 red balls left. The probability of picking a blue ball is 7/14 = 1/2