The average of $10$ numbers is $7$. What will be the new average if each of the numbers is multiplied by $8$?

The daily maximum temperature in Delhi,for $7$ consecutive days in $May, 1988$,were $42.7^{\circ} C, 44.6^{\circ} C, 42.0^{\circ} C, 39.1^{\circ} C, 43.0^{\circ} C, 42.5^{\circ} C$ and $38.5^{\circ} C$. Find out the average daily maximum temperature (in $^{\circ} C$).

The arithmetic mean of $100$ observations is $24$. If $6$ is added to each of the observations and then each of them is multiplied by $2.5$,find the new arithmetic mean.

The mean of marks secured by $50$ students in division $A$ of class $X$ is $61$,$25$ students of division $B$ is $57$,and that of $50$ students of division $C$ is $55$. What will be the mean of marks of the students of three divisions of Class $X$?

The average monthly salary of a staff of $9$ persons is $Rs.\, 2450$. One member of the staff whose monthly salary is $Rs.\, 2650$ is transferred. Find out the average salary of the remaining $8$ persons of the staff (in $Rs.$).

In a set of prime and composite numbers,the number of composite numbers is twice the number of prime numbers,and the average of all the numbers in the set is $9$. If the number of prime numbers and composite numbers are exchanged,then the average of the set of numbers increases by $2$. If,during the exchange of the numbers,the average of the prime numbers and composite numbers individually remained constant,then what was the ratio of the average of composite numbers to the average of prime numbers (initially)?