Sunday, July 19, 2009

Calculating a conditional average

In the real world, a simple average often isn't adequate for your needs.

For example, an instructor might calculate student grades by averaging a series of test scores but omitting the two lowest scores. Or you might want to compute an average that ignores both the highest and lowest values.

In cases such as these, the AVERAGE function won't do, so you must create a more complex formula. The following Excel formula computes the average of the values contained in a range named "scores," but excludes the highest and lowest values:

=(SUM(scores)-MIN(scores)-MAX(scores))/(COUNT(scores)-2)

Here's an example that calculates an average excluding the two lowest scores:

=(SUM(scores)-MIN(scores)-SMALL(scores,2))/(COUNT(scores)-2)

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