There are 4 balls in an urn. Each ball is either red or black. You start by believing that the probabilities that the urn contains 0, 1, 2, 3, 4 red balls are all equal. You then reach into the urn and pull out a ball at random. It is red. Compute the new probabilities that the urn contains 0, 1, 2, 3 or 4 red balls.