Question

Find the mean of the following data by assumed mean method

Class - interval	Frequency
150 - 200	14
200 - 250	26
250 - 300	17
300 - 350	23
350 - 400	20

Answer 1

Let assumed mean 'a' = 275

Class interval	Frequency $f_i$	mid-point $\left(x_i\right)$	Deviation $d_i=x_i-275$	$f_i{d}_{{}_i}$
150 - 200	14	175	-100	-1400
200 - 250	26	225	-50	-1300
250 - 300	17	275	0	0
300 - 350	23	325	50	1150
350-400	20	375	100	2000
	100			450

Hence by assumed mean method using formula
$\overline{x}=a+\frac{1}{h}\sum _{i=l}^5=275+\frac{1}{100}\times 450$
= 275 + 4.50 = 279.50