The average marks of $40$ students in an examination was $25 .$ It was later found that the marks of one student had been wrongly entered as $73$ instead of $37.$ What is the value of correct average

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 $Rs.$ )

The average age of a group of $15$ students is $10 \,years.$ When $5$ more students joined the group, the average got increased by $1\, year.$ The age of the new student is (in $years$)

The average of marks obtained by $120$ candidates in a certain examination is $35 .$ If the average marks obtained by passed candidates are $39$ and those of the failed candidates are $15,$ then what is the number of candidates who passed the examination?

The average of the first $100$ positive integers is

$A , B , C$ and $D$ are four consecutive even numbers respectively and their average is $65 .$ What is the product of $A$ and $D ?$