Question

The mean of the following frequency table is 50. But the frequencies f₁ and f₂ in classes 20 – 40 and 60 – 80 are missing. Find the missing frequencies.

Class interval	0–20	20–40	40–60	60–80	80–100	Total
Frequency	17	f1	32	f2	19	120

Answer 1

Let the assumed mean A = 50 and h = 20.
Calculation of mean

From equations (i) and (ii), we get

Putting the value of f1 in equation (i), we get

Hence, the missing frequencies f₁ is 28 and f₂ is 24.