What is the probability of a leap year selected at random contains 53 Sundays ?

Key insight: A leap year has 366 days, which is 52 full weeks plus 2 extra days.

Those 2 extra days are consecutive weekdays and can be any one of the following seven pairs:

• Monday–Tuesday

• Tuesday–Wednesday

• Wednesday–Thursday

• Thursday–Friday

• Friday–Saturday

• Saturday–Sunday

• Sunday–Monday

Favorable pairs that include Sunday are: Saturday–Sunday and Sunday–Monday, so there are 2 favorable outcomes.

Total equally likely outcomes = 7. Therefore the probability that a randomly selected leap year contains 53 Sundays = 2/7.