Find the mean of the first five prime numbers.

Find the mean and the median of the observations: $72, 15, 28, 31, 32, 51, 44, 43$ and $62$.

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

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 ...........

The mean of $25$ observations is $36$. If the mean of the first $13$ observations is $32$ and the mean of the last $13$ observations is $40$,find the $13^{\text{th}}$ observation.

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.