WAEC 2023 · Paper 1 · Q29

Adu's scores in five subjects in an examination are 85, 84, 83, 86 and 87. Calculate the standard deviation.

Worked solution (try it first)

The mean is $\dfrac{85 + 84 + 83 + 86 + 87}{5} = \dfrac{425}{5}$
$= 85$ .
The deviations from 85 are $0, -1, -2, 1, 2$ , and their squares add up to $0 + 1 + 4 + 1 + 4 = 10$ .
The variance is $\frac{10}{5} = 2$ , so the standard deviation is $\sqrt{2} \approx 1.4$ , option A.