WAEC 2020 · Paper 1 · Q31

Calculate the variance of $\sqrt{2}$ , $(1 + \sqrt{2})$ and $(2 + \sqrt{2})$ .

Worked solution (try it first)

The mean is $\dfrac{3\sqrt{2} + 3}{3} = 1 + \sqrt{2}$ .
The deviations from the mean are $-1$ , $0$ and $1$ , so their squares are $1$ , $0$ and $1$ .
Variance $= \dfrac{1 + 0 + 1}{3} = \dfrac{2}{3}$ , option C.