Question

Observe the following table and find the Mean:

Assumed mean A = 300

Class	Class mark	di = xi – A	Frequency	Frequency × Deviation
	xi	di = xi – 300	fi	fi di
200 – 240	220	– 80	5	– 400
240 – 280	260	– 40	10	– 400
280 – 320	300 `rightarrow` A	0	15	0
320 – 360	340	40	12	480
360 – 400	380	80	8	640
Total			`sumf_i` = 50	`sumf_i d_i` = 320

Answer 1

`sum fi = 50`

`sum fi di = 320`

Assumed mean = A = 300

                                 `overline d = (sum fi di)/ (sum fi)`

                                 = `320/50`

                                 = 6.4 

∴ Mean               `overline X = A + overline d`

                                 = 300 + 6.4

                                 = 306.4

                       Mean = 306.4