Mean and S.D. of a given set of observations is $\displaystyle 1,500$ and $\displaystyle 400$ respectively. If there is an increment of $\displaystyle 100$ in the first year and each observation is hiked by $\displaystyle 20\%$ in $\displaystyle 2$nd years, then find new mean and S.D.

If the range of $\displaystyle 28, 22, 40, 20, 15, 50$ is

If the S.D. of the $\displaystyle 1^{st}$ $\displaystyle n$ natural numbers is $\displaystyle \sqrt{30}$ then the value of $\displaystyle n$ is

If the variance of $\displaystyle 5, 7, 9$ and $\displaystyle 11$ is $\displaystyle 4$, then the coefficient of variation is:

A helicopter flies from A to B at the rate of 500 km/hr. and comes back at the rate 700 km/hr. The average speed of the helicopter is

If Arithmetic Mean (A.M.) and Geometric Mean (G.M.) of two numbers are 6.50 and 6 respectively, then the two numbers are

Which of the following is not a method of dispersion?