The mean of $10$ observations is calculated as $22.7$. It was later noticed that one observation was taken as $15$ instead of $51$ by mistake. Then,the correct mean of the data is ........

The mean of $35$ observations is $42$. Find the sum of those observations $\left(\Sigma f_{i} x_{i}\right)$.

Draw a histogram of the following distribution:

Heights (in $cm$)	Number of students
$150-153$	$7$
$153-156$	$8$
$156-159$	$14$
$159-162$	$10$
$162-165$	$6$
$165-168$	$5$

$A$ grouped frequency table with class intervals of equal sizes using $250-270$ ($270$ not included in this interval) as one of the class intervals is constructed for the following data:
$268, 220, 368, 258, 242, 310, 272, 342$
$310, 290, 300, 320, 319, 304, 402, 318$
$406, 292, 354, 278, 210, 240, 330, 316$
$406, 215, 258, 236$
The frequency of the class $310-330$ is:

Draw a frequency polygon for the following frequency distribution:

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

Draw a histogram for the following frequency distribution with unequal class length:

Class	$0-5$	$5-10$	$10-20$	$20-30$	$30-50$	$50-70$	$70-100$
Frequency	$6$	$8$	$14$	$16$	$24$	$20$	$30$