The term average is a popular one; it is often used, and often used incorrectly.
Although there are different types of averages, the typical definition of the word "average" when talking about a list of numbers is "what you get when you add all the numbers and then divide by how many numbers you have." This statement describes how you calculate the arithmetic mean, or average. But knowing how to calculate a mean doesn't necessarily tell you what it represents.
Let's begin our exploration of the mean: Using your 45 coins, create 9 stacks of several sizes. You must use all 45 coins, and at least 1 coin must be in each of the 9 stacks. It's fine to have the same number of coins in multiple stacks.
Here is one possible arrangement, or allocation, of the 45 coins: