The average marks obtained by a class of $60$ students is $65$. The average marks of half of the students is found to be $85$. The average marks of the remaining students is:

The average age of $A, B, C, D$ five years ago was $45$ years. By including $x$,the present average age of all the five is $49$ years. The present age of $x$ is (in years):

If the average marks of three batches of $55, 60,$ and $45$ students are $50, 55,$ and $60$ respectively,then the average marks of all the students is:

There were $35$ students in a hostel. If the number of students is increased by $7$,the expenditure on food increases by $Rs. \,42$ per day,while the average expenditure per student is reduced by $Rs. \,1$. What was the initial total expenditure on food per day? (in $Rs.$)

$A$ class has $20$ boys and $30$ girls. The average age of boys is $11$ years and that of girls is $12$ years. What is the average age of the whole class in years?

What is the age of a class teacher?
$I.$ There are $11$ students in the class.
$II.$ The average age of the students and the teacher is $14$ years.
$III.$ The average age of the teacher and the students is $3$ years more than that of the students.