JAMB 1992 · UME · Q45

If the scores of 3 students in a test are 5, 6 and 7, find the standard deviation of their scores.

Worked solution (try it first)

The mean is $\frac{5 + 6 + 7}{3} = 6$ .
The deviations from 6 are $-1$ , 0 and 1.
Their squares are 1, 0 and 1, which add up to 2.
The variance is $\frac23$ , and the standard deviation is its square root, $\sqrt{\frac23}$ , option C.