If the mean of $18, 2x, 27, 12, 3x, 5x$ and $21$ is $24,$ then find $x$.

To draw a histogram to represent the following frequency distribution:

Class interval	$5-10$	$10-15$	$15-25$	$25-45$	$45-75$
Frequency	$6$	$12$	$10$	$8$	$15$

The adjusted frequency for the class $25-45$ is:

The class-mark of the class $130-150$ is:

Represent the following data by means of a histogram:

Class	$0-5$	$5-10$	$10-20$	$20-30$	$30-50$	$50-70$
Frequency	$5$	$7$	$12$	$16$	$24$	$16$

The class marks of a frequency distribution are given as follows: $15, 20, 25, \ldots$ The class interval corresponding to the class mark $20$ is:

The marks obtained (out of $100$ marks) by $50$ students in a mathematics test are as given below:
$\begin{array}{lrrrrrrrrr} 10, & 65, & 75, & 37, & 8, & 58, & 35, & 42, & 29, & 52 \\ 19, & 52, & 23, & 61, & 88, & 65, & 18, & 77, & 85, & 49, \\ 12, & 7, & 41, & 75, & 52, & 90, & 30, & 89, & 95, & 62, \\ 16, & 61, & 35, & 68, & 22, & 72, & 56, & 27, & 62, & 93, \\ 25, & 59, & 48, & 81, & 26, & 84, & 60, & 39, & 76, & 50 \end{array}$
Represent the data given above by a grouped frequency distribution table,taking the class intervals as $0-10, 10-20, \dots$ etc.