The proprietor of a men's clothing store has recorded the buying behavior of customers over a long period of time. She has established that the probability that a customer will buy a shirt is about 40%. A customer buys a tie 60% of time when a shirt is purchased, but only 20% of the time when a shirt is not purchased. Suppose that a customer has absolutely no intention of buying a tie. What is the probability that this customer will buy a shirt?