Six numbers have a mean of 5. Five of them are 2, 4, 5, 6 and 9. What is the sixth number?

Explication

Six numbers with a mean of 5 must total 30, and the five known numbers add to 26, so the sixth number is 30 - 26 = 4. Dividing 26 by 5 gives 5.2, which is the mean of the numbers already listed rather than the value still missing from a set of six.