Task 3.1. The day after his birthday, Vasya said: "It's a pity that my birthday this year is not on Sunday, because in that case more guests would have come to me! But Sunday will be the day after tomorrow..." On what day of the week was Vasya's birthday?
Answer: Thursday.

Solution. Since Sunday will be the day after tomorrow, today is Friday. And since today is the day after the birthday, the birthday itself was on Thursday.