[diroussel]

Imagine a hospital where the only patients are either mothers, or babies. All the babies are in the age range zero to 2 months, and the mothers are in the range 16 to 40 years old (mostly). If you compute the average age, it comes out at 12 years old.

What has the average told us? It has told us nothing because it's meaningless with a bi-modal distribution.

For more info read up on the normal distribution, guassian distribution, bi-modal distributions, and the central limit theorem.