Midpoint (Midvalue) of the class $15-30$ is ........

Calculate the mean of the following data:

Class	$4-7$	$8-11$	$12-15$	$16-19$
Frequency	$5$	$4$	$9$	$10$

In the formula $\bar{x} = \frac{\Sigma f_{i} x_{i}}{\Sigma f_{i}}$,$\Sigma f_{i}$ represents ........

Is it correct to say that an ogive is a graphical representation of a frequency distribution? Give reason.

The mean of the following frequency distribution is $28.5$ and the total frequency is $60$. Find the missing frequencies $f_{1}$ and $f_{2}$.

Class	$0-10$	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$
Frequency	$6$	$f_1$	$20$	$15$	$f_2$	$4$

For a given frequency distribution,$n=200$,$\Sigma f_{i} d_{i}=0$ and $A=25$. Then,$\bar{x}=\ldots \ldots \ldots \ldots$