First of all - let's introduce a standard average:

`standard_average_of(a, b, c) = (a + b + c) / 3`

.

We are summing our numbers, and dividing them by amount of numbers summed (imagine distributing what we collectively have equally among us).

But what if we need to equally distribute a set of numbers, where b is mentioned twice?

We could use a formula `(a + b + b + c) / 4`

, or `(a + 2b + c) / 4`

.

This is a `weighted_average_of(a, b, c)`

, where b is weighted twice.