After replacing an old member by a new member, it was found that the average age of five members of a club is the same assit was $3 \,year$ ago. The difference between the ages of the replaced and the new member is ? (in $year$)

A man retired from his service at the age of $60$ He served for $\frac{3}{5}^{ th}$ years of his retirement age. He joined his job at the age of (in $years$)

The average pocket-money of $3$ friends $A, B, C$ is $Rs.\, 80$ $month.$ If $B$ spends double and $C$ spends triple of whate $A$ spends during that month and if the average of their unspent pocketemoney is $Rs.$ $60,$ then $A$ spends (in $Rs.$)

There are two groups $A$ and $B$ of a class, consisting of $42$ and $28$ students, respectively. If the average weight of group $A$ is $25 \,kg$ and that of group $B$ is $40 \,kg ,$ find the average weight of the whole class.

Average age of $15$ students of a class is $15\, years.$ Out of these the average age of $5$ students is $14 \,years$ and that of the other $9$ students is $16\, years.$ The age of the $15^{th}$ student is (in $years$)