WAEC 2019 · Paper 2 · Q7

Statistics & correlation

Age (years)	1–5	6–10	11–15	16–20	21–25	26–30
Number of people	18	12	25	15	20	10

The table shows the age distribution in years of a group of people.

(a)
Using an assumed mean of 13 years, find the mean age of the people.

Worked solution (try it first)

Class marks $3, 8, 13, 18, 23, 28$ and $d = x - 13$ : $-10, -5, 0, 5, 10, 15$ .
$\sum fd = -180 - 60 + 0 + 75 + 200 + 150$
$= 185$ and $\sum f = 100$ .
Mean $= 13 + \dfrac{185}{100} = 14.85$ years.

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