Find the relative frequency of the second class-interval of the frequency distribution.

Class-interval	$70-74$	$75-79$	$80-84$	$85-89$
Frequencies	$3$	$4$	$5$	$8$

The class-mark of a class-interval of a frequency distribution in $m$ and its class-length is $l$. Find its lower and upper class-limits

Determine the third class-interval of the classes $10-19,20-29,.......$ and find its lower and upper class-boundaries.

Define: class-interval.

Define: lower class-limit and upper class-limit.

Define: class-boundary, lower and upper class-boundaries

Define: class-length.

What do you mean by class-frequency? What is relative class-frequency of any class-interval?

What is frequency density of a class-interval? If the class-frequency of the class $19.5-29.5$ be $7$, then what is its frequency density?