JAMB 1997 · UME · Q48

Find the difference between the range and the variance of the numbers 4, 9, 6, 3, 2, 8, 10, 5, 6, 7, where $\sum d^2 = 60$ .

Worked solution (try it first)

The range is the largest number minus the smallest: $10 - 2 = 8$ .
The mean is $\frac{60}{10} = 6$ and $\sum d^2 = 60$ is given, so the variance is $\frac{60}{10} = 6$ .
The difference is $8 - 6 = 2$ , option A.