$10$ years ago, the average age of a family of $4$ members was $24$ $years.$ Two children having been born (with age difference of $2\, years$), the present average age of the family is the same. The present age of the youngest child is (in $years$)

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

The average of $50$ numbers is $38 .$ If two numbers, namely, $45$ and $55$ are discarded, what is the average of the remaining numbers ?

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 marks obtained by $150$ students in an examination is $40 .$ If the average marks of passed students is $60$ and that of the failed students is $20,$ what is the number of students who passed the examination ?

The average of $100$ observations was calculated as $35.$ It was found later, that one of the observations was misread as $83$ instead of $53 .$ The correct average is