Question

The mean of first n odd natural numbers is n2/81, then n =
(a)9
(b)81
(c)27
(d)18

Answer 1

SOLUTION :  

The correct option is (b) : 81

Given : MEAN of First n odd natural numbers is n²/81

First n odd natural numbers are : 1,3,5.........(2n - 1)

MEAN = Sum of all the observations/ Total number of observations

MEAN = (1 + 3 + 5 + ……+ (2n - 1))/n

MEAN = (n/2 ×  (2n)) / n  

[The sum of the first n odd natural numbers : Sn = n/2 (a + l ) = n/2(1 + 2n -1) = n/2 ×2n]

MEAN = n²/n = n  

n²/81 = n  

n² = 81n

n²/n  = 81

n = 81

Hence, the value of n is 81 .  

HOPE THIS ANSWER WILL HELP YOU……

Answer 2

The answer is (b) 81 .
Hope this answer helps....