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All courses Math Foundations · MF.DP.1 55 of 60
Compute and interpret mean, median, range, and interquartile range in context.

Find the mean

Problem
Calculate the mean of 6, 8, 9, and 13.
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Hint

Start by adding the four data values: 6, 8, 9, and 13.

The mean is the total of all values divided by the number of values. There are 4 values here, so divide by 4.

Solution walkthrough

01

Use the mean formula

\[\text{mean}=(\text{sum}~\text{of}~\text{values})/(\text{number}~\text{of}~\text{values})\]

The mean shares the total equally among all data values.

02

Add the data values

\[6+8+9+13=36\]

The four given values have a total of 36.

03

Count the values

\[n=4\]

There are four numbers in the data set, so the total must be divided by 4.

04

Calculate the mean

\[36/4=9\]

Dividing the total by the number of values gives the average.

05

Report the answer

\[9\]

The mean of the four numbers is 9.

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Another way

  1. Balance the values around 9: the deviations -3, -1, 0, and 4 sum to 0, confirming a mean of 9.

!

Common mistake

Do not stop at the sum 36 or divide by 3; the divisor is the count of all four values.