The mean of natural numbers between $1$ to $20$ which are multiples of $3$ is ..........

In the class intervals $10-20$ and $20-30$,the number $20$ is included in:

If the sum of $25$ observations is $900$, find the mean of those observations.

$A$ grouped frequency distribution table with classes of equal sizes using $63-72$ ($72$ included) as one of the class is constructed for the following data:
$30, 32, 45, 54, 74, 78, 108, 112, 66, 76, 88$
$40, 14, 20, 15, 35, 44, 66, 75, 84, 95, 96$
$102, 110, 88, 74, 112, 14, 34, 44$
The number of classes in the distribution will be:

Find the mean,the median,and the mode of the observations:
$33, 92, 55, 90, 35, 77, 58, 41, 80, 64, 46$

Draw a frequency polygon for the following frequency distribution:

Class	$0-10$	$10-20$	$20-30$	$30-40$	$40-50$
Frequency	$6$	$4$	$10$	$12$	$5$