2. In a certain year, there are 5 Saturdays and 4 Sundays in October. Question: What day of the week was October 1st of that year?
2.【Solution】October has 31 days, since there are 5 Saturdays but only 4 Sundays, October 31st must be a Saturday.
Because $31=4 \times 7+3$, so, the 3rd is also a Saturday, and the 1st is a Thursday