The mean of $100$ observations is $50$. If one of the observations which was $50$ is replaced by $150$,the resulting mean will be:

Median of the following numbers: $4, 4, 5, 7, 6, 7, 7, 12, 3$ is

Following is the frequency distribution of total marks obtained by the students of different sections of Class $VIII.$

Marks	$100-150$	$150-200$	$200-300$	$300-500$	$500-800$
Number of students	$60$	$100$	$100$	$80$	$180$

Draw a histogram for the distribution above.

Represent the following data by a bar graph:

Score	Frequency
$1$	$15$
$2$	$13$
$3$	$20$
$4$	$17$
$5$	$20$
$6$	$15$

If the information gathered by an investigator is from an already existing source of data,then such information is called .........

The mean of the following distribution is $50$. Find the value of $a$ and hence the frequencies of $30$ and $70$.

$x$	$f$
$10$	$17$
$30$	$5a+3$
$50$	$32$
$70$	$7a-11$
$90$	$19$