The average of six numbers is $20$. If one number is removed,the average becomes $15$. What is the number removed?

There are $35$ students in a hostel. If the number of students increased by $7$,the expenses of the mess were increased by $Rs. 42$ per day while the average expenditure per head decreased by $Rs. 1$. Find out the actual expenditure of the mess (in $Rs.$).

In a school with $600$ students,the average age of the boys is $12$ $years$ and that of the girls is $11$ $years$. If the average age of the school is $11$ $years$ and $9$ $months$,then the number of girls in the school is:

The average age of $11$ players of a cricket team is increased by $2 \, \text{months}$ when two of them aged $18 \, \text{years}$ and $20 \, \text{years}$ are replaced by two new players. The average age of the new players is?

Last year,$5$ companies had an average of $16$ non-working days each. If $3$ companies had $16$ non-working days each and $2$ companies had $5$ fewer non-working days each,what was the average number of non-working days for these $5$ companies last year?

$A$ batsman has an average of $30$ runs in his $42$ innings. The difference between his maximum and minimum score is $100$. If these two innings are removed,his average for $40$ innings comes down to $28$. What is his minimum score?