Question

Calculate missing frequency, if mean of the distribution is 28.

C.I	0-10	10-20	20-30	30-40	40-50	50-60
Frequency	12	?	27	20	17	6

Answer 1

C.I.	Mid-Point (m)	Frequency (f)	fm
0 − 10 10 − 20 20 − 30 30 − 40 40 − 50 50 − 60	5 15 25 35 45 55	12 ? (f) 27 20 17 6	60 15f 675 700 765 330
		Σf = 82+f	Σfm = 2530+15f

$$\begin{gathered} \overline{X}=28 \\ \overline{X}=\frac{\mathrm{\Sigma }fm}{\mathrm{\Sigma }f} \\ 28=\frac{2530+15f}{82+f} \\ 2296+28f=2530+15f \\ 13f=234 \\ f=\frac{234}{13}=18 \end{gathered}$$
Thus, the missing freuency is 18.