question_answer

  Find mean of the following frequency distribution, using step-deviation-method:          

Classes	0-10	10-20	20-30	30-40	40-50
Frequency	7	12	13	10	8

OR The mean of the following frequency distribution is 25. Find the value of p.

Classes	0-10	10-20	20-30	30-40	40-50
Frequency	2	3	5	3	p

Answer:

  Let assumed mean, a = 25. Here h = 1 0.

Classes	Mid value
0-10 10-20	5 15	7 12	-2 -1
20-30	25	13	0	0
30-40 40-50	35 45	10 8	1 2
		50		0

  and Now Mean,  Mean, OR

Classes	Mid value	Frequency
0-10 10-20 20-30 30-40 40-50	5 15 25 35 45	2 3 5 3 P	10 45 125 105 45p
		13 + p	285 + 45p

Mean,  Hence p = 2