There are two boys participating at an international maths contest in December 2013. One is British and the other is American. They both write their names, the date, and their answers on the paper. The only problem is that they both have the same name and the papers cannot be told apart.
What is the date?
Answer
December 12th, 2013. In America, dates are in Month-Day-Year format whereas in Britain, dates are in Day-Month-Year format, so the day and month must be the same so that they can be changed around with the date remaining the same.