The class marks of a distribution are $6, 10, 14, 18, 22, 26, 30$. The class size is:

Consider the following data:

Daily wage (Rs.)	$30$-$40$	$40$-$50$	$50$-$60$	$60$-$70$	$70$-$80$	$80$-$90$
No. of workers	$17$	$28$	$21$	$15$	$13$	$6$

The coefficient of variation of the above distribution of wages,if its standard deviation is $14.72$,is

There are $n$ observations and all of them are negative numbers. The ascending order of these observations is $x_1, x_2, \ldots, x_n$. If the signs of the first term and last term in that order are changed,then the range of the data is

The mean of a data set comprising $16$ observations is $16$. If one observation with value $16$ is deleted and three new observations with values $3, 4,$ and $5$ are added to the data,then the mean of the resultant data is:

The mean age of $25$ teachers in a school is $40 \text{ years}$. $A$ teacher retires at the age of $60 \text{ years}$ and a new teacher is appointed in his place. If now the mean age of the teachers in this school is $39 \text{ years}$,then the age (in years) of the newly appointed teacher is

The mean of the numbers $a, b, 8, 5, 10$ is $6$ and their variance is $6.8$. If $M$ is the mean deviation of the numbers about the mean,then $25M$ is equal to