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Find the mean deviation about the mean for the data. Height in cms Number of boys 95 - 105 9 105 - 115 13 115 - 125 26 125 - 135 30 135 - 145 12 145 - 155 10

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Question

Find the mean deviation about the mean for the data.

Height in cms Number of boys
95 - 105 9
105 - 115 13
115 - 125 26
125 - 135 30
135 - 145 12
145 - 155 10
Sum
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Solution

Height in cms Mid values xi `d_i (x_i - 130)/10` Frequency fi fidi `|x_i - overline x|` `f_i|x_i - overline x|`
95 - 105 100 −3 9 −27 25.3 227.7
105 - 115 110 −2 13 −26 15.3 198.9
115 - 125 120 −1 26 −26 5.3 137.8
125 - 135 130 0 30 0 4.7 141.0
135 - 145 140 1 12 12 14.7 176.4
145 - 155 150 2 10 20 24.7 247.0
Sum - - 100 −47 - 1128.8

Mean `overline x = a +((sumf_i d_i)/(sumf_i)) xx h`

= `130 + ((-47)/100) xx 10`

= 130 − 4.7

= 125.3

Mean Deviation = `(sumf_i |x_i -  overline x|)/N`

= `1128.8/100`

= 11.288

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Chapter 13: Statistics - EXERCISE 13.1 [Page 271]

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NCERT Mathematics [English] Class 11
Chapter 13 Statistics
EXERCISE 13.1 | Q 10. | Page 271

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