[Taken from Thinking Mathematically, p. 160. Modified by Sam Rebelsky]
Noted cartoon character Churchy LaFemme is terrified of Friday the 13th, particularly when it falls on Fridays. (He claims that like many holidays, birthdays, and other special days, Friday the 13th can fall on any day of the week.) He's worried that Friday the 13th will fall on Fridays more often than he can cope with.
How many times will Friday the 13th occur on a Friday this year? What is the maximum number of times Friday the 13th can occur on a Friday in a calendar year, using the standard calendar? The least number of times? Does it matter whether you start in January or another month?