In this section the average or arithmetic mean and the weighted average are defined.

• The *average* and the *arithmetic mean* are equivalent.

• To find the average of a group of numbers, add all of the numbers together and divide the sum by how many numbers there are.

• **Example:** What is the average of {5, 6, 9, 25}?

The total sum is:

5 + 6 + 9 + 25 = 45

Divide the sum by how many numbers there are, or 4.

45 ÷ 4 = 11.25

• **Example:** What is the average of {9, 6, ...

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