Question

17. If the mean of first ‘n' natural numbers is 11, then n=
1)22
2)12
3)21​

Answer 1

$\huge \dag \boxed{ \mathfrak \purple{Answer}}$

Mean =

$\sf \frac{sum \: of \: n \: natural \: numbers} { n }$

$\sf\frac{ = n(n+1) }{ 2n }$

ATQ , 

$\sf \frac{n(n+1)}{ 2n} = 11$

n²+ n = 22n

n² - 22n + n = 0 

n² - 21 n = 0

n(n-21) = 0 

n = 0 

or n = 21