Two numbers have a mean of 12. One of them is 10. What is the other number?

Explication

Two numbers with a mean of 12 must total 24, so the other number is 24 - 10 = 14. Answering 2 gives the gap between 10 and the mean rather than the number itself, because the second number has to sit the same distance above the mean as the first sits below it.