Find the average of first $25$ multiples of $5$.

$A$ batsman scores $87$ runs in the $21^{st}$ match of his career. His average runs per match increase by $2.$ What is his average before the $21^{st}$ match?

Out of four numbers,whose average is $60$,the first one is one-fourth of the sum of the last three. The first number is

The average age of Sachin $(S)$ and Ganguli $(G)$ is $35 \text{ years}$. If Kaif $(K)$ replaces Sachin,the average age becomes $32 \text{ years}$,and if Kaif $(K)$ replaces Ganguli $(G)$,the average age becomes $38 \text{ years}$. If the average age of Dhoni $(D)$ and Irfan $(I)$ is half of the average age of Sachin,Ganguli,and Kaif,then the average age of all the five people is:

The average salary per head of all the workers in a workshop is $Rs. 850$. If the average salary per head of $7$ technicians is $Rs. 1000$ and the average salary per head of the rest is $Rs. 780$,find out the total number of workers in the workshop.

The average salary of $20$ workers in an office is $Rs. 1900$ per month. If the manager's salary is added,the average becomes $Rs. 2000$ per month. The manager's annual salary (in $Rs.$) is