3. The Instagram page of the Math Olympics publishes a problem every day. Alberto and Barbara challenge each other to solve the most problems over a period of 10 weeks, starting from a Monday. Barbara knows that Alberto tries to solve all and only the problems from Monday to Thursday each week (but she doesn't know if he succeeds or not). Barbara, on the other hand, is sure she can solve all the problems except those on Sunday. Assuming Barbara is right and considering that she intends to start working as late as possible, which day of the week should she start to be sure of her victory?
(A) Monday
(B) Tuesday
(C) Wednesday
(D) Thursday
(E) Friday
(3) The correct answer is $(B)$.

Since Alberto can solve at most 4 problems each week, in 10 weeks he can solve at most 40. To be certain of solving at least 41 problems, Barbara needs 6 weeks and 5 days of work, starting from the last day. She must therefore start on a Tuesday.

Question proposed by Riccardo Zanotto.