what is the probability of having 5 sundays in december

Answer 1

Look at the first day of the month. If a January begins on a Friday, Saturday, or Sunday then that January will have 5 Sundays. Therefor January has a 3/7ths chance of having 5 Sundays.

This question goes further into leap years. Every 400 years the calendar repeats, which is why 2000 was a leap year and 1900 was not. In this 400 year cycle January begins on Friday(58), Saturday(56), or Sunday(58) times for a proportion of 172/400.

Essentially these are the same answers though 3/7 = 0.4286 and 172/400 = 0.43, so it really depends on how your teach would like you to look at the problem.