Find the mean of the observations $15, 22, 18, 27, 31, 21, 14, 36, 25$ and $34$.

When the investigator has personally obtained the information for a particular purpose,this data is called ........ data.

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

The following table gives the frequencies of most commonly used letters $a, e, i, o, r, t, u$ from a page of a book:

Letters	$a$	$e$	$i$	$o$	$r$	$t$	$u$
Frequency	$75$	$125$	$80$	$70$	$80$	$95$	$75$

Represent the information above by a bar graph.

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

The observation which is repeated most often in an ungrouped data is called .......... of the data.