JAMB 1993 · UME · Q49

Calculate the standard deviation of the data 7, 8, 9, 10, 11, 12, 13.

Worked solution (try it first)

There are 7 values and they add up to 70, so the mean is 10.
The deviations are $-3$ to 3.
Their squares are 9, 4, 1, 0, 1, 4, 9, which add up to 28.
The variance is $\frac{28}{7} = 4$ , so the standard deviation is $\sqrt4 = 2$ , option A.