Usually when you calculate an average, all of the numbers are given equal significance; the numbers are added together, and then, divided by the number of numbers. With a Weighted Average, one or more numbers is given a greater significance, or weight.
Find a Weighted Average
Use the SUMPRODUCT and the SUM functions to find a Weighted Average, which depends on the weight applied to the values.
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For example, a shipment of 10 cases of pencils is 20 cents per case. But a second shipment of 40 cases costs 30 cents per case, because pencils are in high demand. If you averaged the cost of each shipment this way (0.20+0.30)/2 = 0.25, the result isn’t accurate.
The math doesn’t take into account that there are more cases being sold at 30 cents than at 20 cents. To get the correct average, use this formula to get the result (28 cents per shipment):
=SUMPRODUCT(A2:A3,B2:B3)/SUM(B2:B3)
The formula works by dividing the total cost of the two orders by the total number of cases ordered.
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Usually when you calculate an average, all of the numbers are given equal significance.
The numbers are added together and then divided by the number of numbers, as in this example, which returns an unweighted average of 5.
With a Weighted Average, one or more numbers is given a greater significance, or weight.
In this example, the Mid-term and Final exams have a greater weight than Tests 1 and 2.
We’ll use the SUMPRODUCT and SUM functions to determine the Weighted Average.
The SUMPRODUCT function multiplies each Test’s score by its weight, and then, adds these resulting numbers.
We then divide the outcome of SUMPRODUCT by the SUM of the weights.
And this returns the Weighted Average of 80.
SUMPRODUCT is essentially the Sum of Test 1 times its weight, plus the Mid-term times its weight, and so on.
To get the Weighted Average, you divide by the Total of the weights.
If we had just averaged the Test scores, the value would be 75.5, a significant difference.
For more information about the SUMPRODUCT and SUM functions, see the course summary.
Now, you have a good idea about how to average numbers in Excel.
Of course, there’s always more to learn.
So, check out the course summary at the end, and best of all, explore Excel 2013 on your own.
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