Obtain the mean of the following distribution:

Frequency $(f_i)$	Variable $(x_i)$
$4$	$4$
$8$	$6$
$14$	$8$
$11$	$10$
$3$	$12$

The mean of the data $\frac{4}{7}, \frac{4}{9}, \frac{3}{7}, \frac{5}{9}$ is ........

Heights (in $cm$) of $30$ girls of Class $IX$ are given below:
$140, 140, 160, 139, 153, 153, 146, 150, 148, 150, 152$
$146, 154, 150, 160, 148, 150, 148, 140, 148, 153, 138$
$152, 150, 148, 138, 152, 140, 146, 148$
Prepare a frequency distribution table for this data.

For the following data,draw a frequency polygon:

Class	$10-20$	$20-30$	$30-40$	$40-50$	$50-60$	$60-70$	$70-80$
Frequency	$1$	$4$	$5$	$10$	$5$	$4$	$1$

In a histogram, the areas of the rectangles are proportional to the frequencies. Can we say that the lengths of the rectangles are also proportional to the frequencies?

The width of the class $50.5-55.5$ is .............