Sometimes the answer is easy but the question is hard. The Mad Hatter doesn't really present this puzzle in Alice in Wonderland, but he might have. Lewis Carroll (1832-1898) was obsessed by the ambiguity of words and the notion of time out of joint. Lanky and sensitive, Charles Dodgson (his real name) was a mathematics lecturer at Oxford, but gained fame as a writer of stories for children, witty, complex and full of puzzles.

Here's a more serious puzzle you can try yourself. Back home, the clock on the wall of the Mad Hatter's house loses two minutes an hour. A table clock gains two minutes an hour on the wall clock. The alarm clock falls two minutes an hour behind the table clock, and the Mad Hatter's wristwatch gains two minutes on the alarm clock every hour. When he left for the tea party at noon all the clocks were set to the correct time. What time, to the nearest minute, will the wrist watch show when he arrives home seven hours later?