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CLASS_11_MATHS_SOLUTIONS_NCERT

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Class XI Chapter 15 – Statistics Maths<br />

______________________________________________________________________________<br />

Solution 8:<br />

The given observations are already in ascending order.<br />

Adding a column corresponding to cumulative frequencies of the given data, we obtain the<br />

following table.<br />

x<br />

i<br />

f cf . .<br />

i<br />

15 3 3<br />

21 5 8<br />

27 6 14<br />

30 7 21<br />

35 8 29<br />

Here, N = 29, which is odd.<br />

th<br />

th<br />

observation =15 observation<br />

77<br />

Median=<br />

<br />

2<br />

<br />

<br />

This observation lies in the cumulative frequency 21, for which the corresponding observation<br />

is 30.<br />

∴ Median = 30<br />

The absolute values of the deviations from median, i.e.<br />

xi<br />

M, are<br />

xa "M 15 9 3 0 5<br />

i<br />

i<br />

f 3 5 6 7 8<br />

f xa "M 45 45 18 0 40<br />

i<br />

i<br />

5 5<br />

f 29, f x M 148<br />

i i i<br />

i1 i1<br />

1<br />

5<br />

1<br />

<br />

i i<br />

i1<br />

M.D. M f x M 148 5.1<br />

N 29<br />

Question 9:<br />

Find the mean deviation about the mean for the data.<br />

Income per day<br />

Number of persons<br />

0-100 4<br />

100-200 8<br />

200-300 9<br />

300-400 10<br />

400-500 7<br />

500-600 5<br />

600-700 4<br />

700-800 3<br />

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