91Ó°ÊÓ

The mean is equal to the sum of all data values divided by the number of data values.

The standard deviation is a calculated value that shows how the data deviates from the mean of the data.

The variance of the data is the square of the standard deviation.

The set of data are:

15, 16, 16, 15, 16, 17, 18

Calculate the mean of the data.

Mean$$\begin{gathered} =\frac{15+16+16+15+16+17+18}{7} \\ =\frac{113}{7} \\ ≈16.1 \end{gathered}$$

To find the variance, subtract the mean from each data and then square it and add and then divide by the numbers of data.

The variance is

$$\begin{gathered} =\frac{{\left(15−16.1\right)}^2+{\left(16−16.1\right)}^2+{\left(16−16.1\right)}^2+{\left(15−16.1\right)}^2+{\left(16−16.1\right)}^2+{\left(17−16.1\right)}^2+{\left(18−16.1\right)}^2}{7} \\ =\frac{6.87}{7} \\ ≈1 \end{gathered}$$

To find the standard deviation, square root the variance.

The standard deviation is

$$\begin{gathered} =\sqrt{1} \\ =1 \end{gathered}$$

Therefore, the mean is 10.8, the variance is 1 and the standard deviation is 1.