Averaging negative numbers is very similar to averaging positive ones. You still find the sum of the numbers and divide that sum by the number of terms, but with negative numbers you will also need to determine whether the number produced by each step is positive or negative.

Add the numbers together.
For example, if you need to find the average of 2, 3, 4 and 1, adding these numbers will give you 10. Remember that the sum of a series of negative numbers is always negative.

Count the number of terms (numbers) that you added. In the example, there were four numbers. Counted numbers are always positive, so the answer to this step is positive 4.

Divide the sum by the number of terms. The answer is called the arithmetic mean, or average, of these numbers.
In the example problem, 10 / 4 = 2.5.
Tips & Warnings
 Do not forget that your sum is negative, but the number of terms is positive. A negative divided by a positive always yields a negative answer.
References
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