Mean (Average)
The mean (average) is found by adding all the values in a data set and dividing by how many values there are.
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Because every single value contributes equally to the mean, it gives the most complete picture of the data — but that also makes it sensitive to extreme values. Use the mean for symmetric data with no extreme values.
The GED & HiSET also test the missing-value technique: work the mean formula backward. The required sum equals Mean × Count. Then subtract the sum of the known values to find the missing one — multiply, don’t divide.
Watch out for outliers. A single extreme value pulls the mean far from where most of the data sits, which can make it a misleading description of a “typical” value; in that case the median is usually the better measure.
Worked example
The mean of 5 test scores is 84. Four of the scores are 78, 82, 90, and 91. Find the missing score.
- Work backward: if the mean is 84 and there are 5 values, the total must be 84 × 5 = 420.
- Find the sum of the four known scores: 78 + 82 + 90 + 91 = 341.
- Subtract to find the missing score: 420 − 341 = 79.
- Check: (78 + 82 + 90 + 91 + 79) ÷ 5 = 420 ÷ 5 = 84.
The missing score is 79.
On the test: The words “typical” or “best represents” signal that you need to choose the right measure, not just calculate one.
This concept also comes up in Data Analysis.
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