If the covariance between x and y is 30, variance of x is 25 and variance of y is 144, then what is the correlation coefficient?

A random sample of 20 people is classified in the following table according to their ages.

Age	Frequency
15-25	2
25-35	4
35-45	6
45-55	5
55-65	3

What is the mean age of this group of people?

What is the mean deviation from the mean of the numbers 10, 9, 21, 16, 24 ?

If the total number of observations is 20, $$\sum {x_i^{}} $$ = 1000 and $$\sum {x_i^2} $$ = 84000, then what is the variance of the distribution?