NCERT Class XI Mathematics - Statistics - Solutions

Question : 11

Total: 34

Find the mean deviation about median for the following data :

Marks	0 - 10	10 – 20	20 – 30	30 – 40	40 – 50	50 – 60
Number of girls	6	8	14	16	4	2

Solution:

Marks	Mid values xi	fi	c.f.	\|xi−27.86\|	fi\|xi−27.86\|
0 - 10	5	6	6	22.86	137.16
10 - 20	15	8	14	12.86	102.88
20 - 30	25	14	28	2.86	40.04
30 - 40	35	16	44	7.14	114.24
40 - 50	45	4	48	17.14	68.56
50 - 60	55	2	50	27.14	54.28
		50			517.16

Here,

= 25
∴ Median class is 20 – 30
Median(M) = 20 +

25−14

× 10 = 20 + 7.86 = 27.86
∴ M.D. about median =

i=1

fi|xi−M| =

× 517.16 = 10.34

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