Question

If the standard deviation of first n natural numbers is 2, then the value of n is

• A. 6
• B. 7
• C. 5
• D. 4

Answer 1

Answer: (B)

7

Answer 2

standard deviation of first n natural number =$\sqrt {\frac {n^2-1}{12}}$
Given standard deviation of first n natural number = 2
2=$\sqrt {\frac {n^2-1}{12}}$
4=$\frac {n^2-1}{12}$
48=n2-1,
n2=49
n=7
Therefore, the correct option is (B) 7