The median of the first ten natural numbers is .........

Is it correct to say that in a histogram,the area of each rectangle is proportional to the class size of the corresponding class interval? If not,correct the statement.

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

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

Draw a histogram to represent the following grouped frequency distribution:

Ages (in years)	Number of teachers
$20-24$	$10$
$25-29$	$28$
$30-34$	$32$
$35-39$	$48$
$40-44$	$50$
$45-49$	$35$
$50-54$	$12$

State whether each of the following statements is true or false:
$(1)$ The mean of the first four odd natural numbers is $4$.
$(2)$ The highest value of the data is called a range.
$(3)$ The mean of $30$ observations is $30$,then the sum of those observations is $60$.

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 ........