The February page of a leap year is shown. If a leap year is picked at random, what is the probability that it has 53 Sundays?

A leap year has 52 weeks + 2 days. The two extra days are one of 7 equally likely pairs: (Sun, Mon), (Mon, Tue), …, (Sat, Sun). Sunday appears in 2 of them, so the probability is 2/7. (1/7 is the answer for an ordinary year.)