A girl has been assigned to window cleaning for the day. She has to clean three windows, all different sizes. However, the girl is very pale and burns easily, so she wants to decide which SPF factor to use. She begins cleaning at 12:00 in the morning and can clean 1 square metre in 1 minute. The first window is 10′ by 10′, the second 9′ by 16′, and the third 9′ by 20′. Assuming that any SPF sunscreen is available, which one should she buy?
Answer
0. She starts at 12:00 in the morning, or midnight. At that time, the sun isn’t up yet.
