JAMB 1992 · UME · Q43

If the mean of the frequency distribution below is 5.2, find $y$ .

$x$	2	4	6	8
$f$	4	$y$	6	5

Worked solution (try it first)

Total frequency: $4 + y + 6 + 5 = 15 + y$ .
Total of $fx$ : $8 + 4y + 36 + 40 = 84 + 4y$ .
Mean $= \frac{\sum fx}{\sum f}$ , so $\frac{84 + 4y}{15 + y} = 5.2$ and $84 + 4y = 78 + 5.2y$ .
Collect terms: $6 = 1.2y$ , so $y = 5.0$ , option C.