The class mark of the class $90-120$ is:

Find the number of observations,if the sum of some observations is $975$ and their mean is $32.5$.

The mean of $100$ observations is $50$. If one of the observations which was $50$ is replaced by $150$,the resulting mean will be:

The class mark of a frequency distribution with equal sizes of two successive classes is $72$ and $77$. Then,the width of the class is ...........

Convert the given frequency distribution into a continuous grouped frequency distribution:

Class interval	Frequency
$150-153$	$7$
$154-157$	$7$
$158-161$	$15$
$162-165$	$10$
$166-169$	$5$
$170-173$	$6$

In which intervals would $153.5$ and $157.5$ be included?

The frequency distribution is given below:

Marks	$0-20$	$20-40$	$40-60$	$60-100$
Number of Students	$10$	$15$	$20$	$25$

This distribution has been represented graphically as shown in the image. Is this representation correct? Explain.