The range of the observations: $7, 9, 7, 5, 6, 6, 9, 18, 8, 8, 6$ is ..........

The mean of $10$ observations is $52$. If $12$ is subtracted from each observation,then the mean of the new observations so obtained is:

The blood groups of $30$ students are recorded as follows:
$A, B, O, A, AB, O, A, O, B, A, O, B, A, AB, B, A, AB, B$
$A, A, O, A, AB, B, A, O, B, A, B, A$
Prepare a frequency distribution table for the data.

The observations $56, 58, 63, x-5, x+1, 75, 81, 85$ have been arranged in ascending order. If the median of the data is $67$,find the value of $x$.

Draw a frequency polygon for the following frequency distribution:

Class	$20-30$	$30-40$	$40-50$	$50-60$	$60-70$	$70-80$
Frequency	$5$	$7$	$12$	$7$	$10$	$9$

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 ...........