NECO 2022 · Paper 1 · Q53

Dispersion & cumulative frequency

The mean of the following set of data: 5, 7, 9, $x$ and 6 is 6. Find the variance.

Worked solution (try it first)

From the mean, $x = 3$ , so the data are 5, 7, 9, 3, 6 with mean 6.
The deviations from 6 are $-1, 1, 3, -3, 0$ .
Their squares add up to $1 + 1 + 9 + 9 + 0 = 20$ .
Variance $= \dfrac{20}{5} = 4.0$ , option B.

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