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Mean (average)

To find the mean (the average), add up all the values and divide by how many there are: 15, 7, 8, 13 and 7 add up to 50, and 50 ÷ 5 = 10.

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Ana sold 15 and Luis 7. If 5 of Ana's sales get credited to Luis, what happens to the team's average?

A sales team over one week. Example data.

How to work it out: add up all the values and divide by how many there are. In Excel: =AVERAGE(B2:B6). Mean and average name the same number; the full name is the arithmetic mean.

Think of it as sharing out evenly: the average is what each person would get if the total were split into equal parts, as in the figure. That's why one very large value pulls it up: the total grows, and so does everyone's share.

When there are outliers, the median describes the typical case better. When some values count more than others, use a weighted average. And to see how far from the average the data falls, look at the standard deviation.

Practice it in Is the average salary what most people earn? and Can you average percentages?.

How it's used

How to work out the average

Quiz scores out of 10: 8, 9, 7, 10

  1. Add them up: 8 + 9 + 7 + 10 = 34
  2. Count them: 4
  3. marked: Divide: 34 ÷ 4 = 8.5
  4. In Excel: =AVERAGE(B2:B5)It adds and counts for you.
Count values, not cells: =AVERAGE skips blanks. If some values count more than others (credits, pounds, hours), you want a weighted average.

When to look closer

The blank cell and the zero

B2:B6 = 9, 8, (blank), 10, 9

  1. marked: =AVERAGE(B2:B6)
  2. 9

With the cell blank, the average is 9. If you type 0 in it, what do you think happens?

Ask your Maestro about Mean

It answers from the free course page closest to this word, the way it answers while you study.

Example

You: What does "Mean" mean, in plain words?

Your Maestro: I'll explain it with a case of yours: it sticks better than a definition. Which average at work gets dragged by one very large value?

Asking about: Answers from the page "Is the average salary what most people earn?"

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Related terms

  • Median

    The median is the middle value when you sort the data from lowest to highest: half sit below it and half above. In Excel you get it with =MEDIAN(B2:B11).

  • Weighted average

    A weighted average gives each value a weight for how much it counts, instead of treating them all the same: multiply each value by its weight, add them up and divide by the sum of the weights.

  • Outlier

    An outlier is a value that sits far from the rest, like a $9,800 order among $300 ones. It can be a data-entry error or a real, important case: before you drop it, find out which.

  • Standard deviation

    Standard deviation measures how far data lands from the average: with an average of 30 and an SD of 2, most values fall from 28 to 32. In Excel: =STDEV.S.

The whole glossary