Mathematics

Using assumed mean method, calculate the mean.
Class-interval Frequency
0-30 22
30-60 30
60-90 40
90-120 36
120-150 28
150-180 20

Statistics

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Answer

Class-interval	Frequency (f)	Class mark (x)	d = x - A	fd
0-30	22	15	-60	-1320
30-60	30	45	-30	-900
60-90	40	A = 75	0	0
90-120	36	105	30	1080
120-150	28	135	60	1680
150-180	20	165	90	1800
Total	Σf = 176			Σfd = 2340

By formula,

Mean = A + $\dfrac{Σfd}{Σf}$

= 75 + $\dfrac{2340}{176}$

= 75 + 13.30

= 88.30

Hence, mean = 88.30

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