What is the median of the six numbers 1, 3, 5, 7, 9 and 11?

Explication

The six numbers are in order, and the two central positions hold 5 and 7, so the median is their mean, 6. Answering 5 or 7 keeps one of those two numbers, but with an even count the median lies between them and need not be a number that appears in the list at all.