Sanya knows that 1st January of a particular reference year, which she calls Year Y, fell on a Monday. Year Y is a leap year. She wants to work out which day of the week various dates fall on, both within Year Y itself and in the years following it, using the standard rule that an ordinary year has 365 days, made up of 52 complete weeks plus 1 extra "odd day," while a leap year has 366 days, made up of 52 complete weeks plus 2 extra "odd days." Years Y+1, Y+2, and Y+3 are all ordinary years, while Year Y+4 is again a leap year.

Separately, within Year Y itself, Sanya wants to work out the day of the week for the 1st of several other months, given that January has 31 days, February (since Year Y is a leap year) has 29 days, March has 31 days, and April has 30 days.