A classic test lets a monkey choose M&Ms until the researcher identifies three colors (say blue, red, and green) that the monkey seems to prefer about equally. The monkey is then offered a choice between two M&Ms—say, blue and red. If the monkey chooses blue, then the monkey is offered a choice between red and green. Two-thirds of the time, the monkey chooses green, apparently confirming the theory of choice rationalization: after we reject something, we devalue it.

Now suppose that the monkey is not perfectly indifferent between blue, red, and green M&Ms, but in fact prefers blue to red. What is the probability that the monkey also prefers green to red? (Assume that the monkey is randomly chosen from a group of monkeys that are equally likely to prefer one color to another.)