JAMB 2000 · UME · Q42

If the mean of the numbers $0$ , $x + 2$ , $3x + 6$ and $4x + 8$ is 4, find their mean deviation.

Worked solution (try it first)

The four numbers add up to $8x + 16$ , and their mean is 4, so $8x + 16 = 16$ and $x = 0$ .
The numbers are 0, 2, 6 and 8.
Their distances from 4 are 4, 2, 2 and 4, which add up to 12.
The mean deviation is $\frac{12}{4} = 3$ , option C.