JAMB 2012 · UTME · Q46

Find the standard deviation of 2, 3, 8, 10 and 12.

Worked solution (try it first)

The numbers add up to 35, so the mean is 7.
The deviations are $-5$ , $-4$ , 1, 3, 5.
Their squares are 25, 16, 1, 9, 25, which add up to 76.
The variance is $\frac{76}{5} = 15.2$ , so the standard deviation is $\sqrt{15.2} \approx 3.9$ , option A.