The average monthly salary of $20$ employees in an organisation is $Rs. 1500$. If the manager's salary is added, then the average salary increases by $Rs. 100$. What is the manager's monthly salary (in $Rs.$)?

The average height of the students of a class of $20$ is $105 \, cm$. If ten more students of average height of $120 \, cm$ join this class,the average height of the class will become (in $cm$)?

The average of $50$ numbers is $30.$ If two numbers,$35$ and $40$ are discarded,then the average of the remaining numbers is nearly.

The average weight of $A, B$ and $C$ is $84 \, kg$. If $D$ joins,the average weight now is $80 \, kg$. If another person $E$,who is $3 \, kg$ heavier than $D$,replaces $A$,then the average weight of $B, C, D$ and $E$ becomes $79 \, kg$. What is the weight of $A$ in $kg$?

The average salary of all the staff in an office of a corporate house is $Rs. 5,000$. The average salary of the officers is $Rs. 14,000$ and that of the rest is $Rs. 4,000$. If the total number of staff is $500$,what is the number of officers?

$A$ batsman has a certain average in $11$ innings. In the $12^{\text{th}}$ innings,he scores $90$ runs and his average decreases by $5$. After the $12^{\text{th}}$ innings,what is his average?