Blue Island is a tourist attraction that can only be reached by ferry. Tourists may visit the island on any day but they must return to the mainland on the same day. Ferries leave the mainland every 40 minutes. The first ferry leaves at 09:00 and the last ferry leaves at 15:00. Ferries leave Blue Island to return to the mainland at 11:00, 12:00, 13:00 and then every 30 minutes until 17:00. The ferry journey in either direction takes 15 minutes. Kenny catches the first ferry from the mainland to Blue Island after 12:00 and wants to spend at least three hours on the island. a) What is the earliest time that he can expect to arrive back on the mainland?

Each ferry can carry at most 30 tourists.

b) Explain why not every ferry on any given day can carry a full load of tourists.

Last Monday each ferry carried at least 5 tourists
c) (i) What was the greatest possible number of tourists on Blue Island at 11:30?
c) (ii) What was the possible number of tourists on Blue Island at 11:30?