Question

Calculate mean of the following data:

Marks Below	:	10	20	30	40	50	60	70
No. of Students	:	5	9	17	29	45	60	70

Answer 1

Marks	Mid Value (m)	f	fm
0 − 10 10 − 20 20 − 30 30 − 40 40 − 50 50 − 60 60 − 70	5 15 25 35 45 55 65	5 9 − 5 = 4 17 − 9 = 8 29 − 17 = 12 45 − 29 = 16 60 − 45 = 15 70 − 60 = 10	25 60 200 420 720 825 650
		Σf = 70	Σfm = 2900

For the calculation of mean, first the given less than series is converted in continuous series as above.

$\overline{X}=\frac{\mathrm{\Sigma }fm}{\mathrm{\Sigma }f}=\frac{2900}{70}=41.42$
Thus, the mean marks is 41.42.