Part 1: An urn contains 100 balls, 50 are red and 50 are black. Two balls are drawn without replacement. 1. What is the probability of having two red balls ? 2. What is the probability of having one red ball and one black ball ?

Part 2: We now have two urns. Urn 1 contains 90 black balls and 10 red balls, urn 2 contains 10 black balls and 90 red balls. Two balls are drawn without replacement.

1. What is the probability of having two red balls if you choose to take both balls in the same urn ? 2. What is the probability of having two red balls if you choose to draw a ball in each urn ? 3. Two balls have been drawn from the same urn and we got two red balls. What is the probability of having chosen urn 2 ?