WAEC 2019 · Paper 2 · Q6

Wages ($)	40–49	50–59	60–69	70–79	80–89	90–99	100–109	110–119
Number of employees	4	12	14	11	7	5	2	1

The table shows the distribution of wages earned by employees in a company.

Worked solution (try it first)

Class marks $44.5, 54.5, \ldots, 114.5$ and $d = x - 74.5$ : $-30, -20, -10, 0, 10, 20, 30, 40$ .
$\sum fd = -120 - 240 - 140 + 0 + 70 + 100 + 60 + 40$
$= -230$ and $\sum f = 56$ .
Mean $= 74.5 + \dfrac{-230}{56}$
$= 74.5 - 4.107$
$\approx 70.39$ , so the mean wage is $70.39.