5. On a certain island, the climate is unusually regular: it always rains on Mondays and Fridays, and there is fog on Saturdays, while the rest of the days are sunny. On which day of the week should a group of tourists start their vacation if they want to stay for 30 days and catch as many sunny days as possible?
Solution: Let's find out how many full weeks are in 30 days. We get 4 weeks. During these weeks, the number of sunny days does not depend on when the vacation starts. For the remaining two days, we choose Thursday and Friday - sunny days. Therefore, we send the tourists in the morning on Thursday.

Answer: on Thursday.