Statistics Test...

Calculate the standard deviation of the following data.
$$10, 20, 15, 8, 3, 4$$

Which one of the following is a measure of dispersion?

The mean and the variance of $$10$$ observations are given to be $$4$$ and $$2$$ respectively. If every observation is multiplied by $$2$$, the mean and the variance of the new series will be respectively.

Find the variance of the following distribution.

If $$n=10, \bar{x}=12$$ and $$\sum x^2=1530$$, then calculate the coefficient of variation.

Calculate the standard deviation of the following data.

The variance of $$20$$ observations is $$5$$. If each observation is multiplied by $$2$$, then what is the new variance of the resulting observations?

What is the combined standard deviation of all 250 items ?

The variance of numbers $$x_1, x_2, x_3,..... x_n$$ is V. Consider the following statements : 
1. If every $$x_1$$, is increased by 2, the variance of the new set of numbers is V.
2. If the numbers $$x_1$$ is squared, the variance of the new set is $$V^2$$.
Which of the following statements is/are correct ?

Let X denote the number of scores which exceed 4 in 1 toss of a symmetrical die. Consider the following statements :
1. The arithmetic mean of X is 6.
2. The standard deviation of X is 2.
Which of the above statements is/are correct ?