If mean deviation about mean of numbers 1,2,3, ldots ., n , where n is odd, is frac{5(n+1)}{n} , the

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13.Statistics

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If the mean deviation about the mean of the numbers $1,2,3, \ldots ., n$, where $n$ is odd, is $\frac{5(n+1)}{n}$, then $n$ is equal to

A

$20$

B

$25$

C

$23$

D

$21$

(JEE MAIN-2022)

Solution

Mean deviation about mean of first $n$ natural numbers is $\frac{ n ^{2}-1}{4 n }$

$\therefore n =21$

Standard 11

Mathematics

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