The mean of $3, -3, -3, 3, 3, -3$ is ..........

The class mark of the class $70-90$ is ...........

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

Class	$0-10$	$10-20$	$20-40$	$40-70$	$70-100$
Frequency	$15$	$13$	$28$	$36$	$27$

Ten observations $6, 14, 15, 17, x+1, 2x-13, 30, 32, 34, 43$ are written in an ascending order. The median of the data is $24$. Find the value of $x$.

Prepare a continuous grouped frequency distribution from the following data:

Mid-point	Frequency
$5$	$4$
$15$	$8$
$25$	$13$
$35$	$12$
$45$	$6$

Also,find the size of the class intervals.

The following table shows a frequency distribution for the speed of cars passing through a particular spot on a highway:

Class interval $(km/h)$	Frequency
$30-40$	$3$
$40-50$	$6$
$50-60$	$25$
$60-70$	$65$
$70-80$	$50$
$80-90$	$28$
$90-100$	$14$

Draw a histogram and a frequency polygon representing the data above.