$A$ man retired from his service at the age of $60$. He served for $\frac{3}{5}$ of his retirement age. At what age (in $years$) did he join his job?

$A$ group of boys has an average weight of $36 \,kg$. One boy weighing $42 \,kg$ leaves the group and another boy weighing $30 \,kg$ joins the group. If the average now becomes $35.7 \,kg$,then how many boys are there in the group?

The average weight of five persons sitting in a boat is $38\, kg$. The average weight of the boat and the persons sitting in the boat is $52\, kg$. What is the weight of the boat (in $kg$)?

On $24^{\text{th}}$ May,$2008$,the maximum temperatures of Delhi,Kolkata,and Mumbai were recorded as $35^{\circ}C$,$33^{\circ}C$,and $34^{\circ}C$ respectively. What was the maximum temperature of Chennai so that the average maximum temperature of those four cities would be $35^{\circ}C$ (in $^{\circ}C$)?

The average age of a cricket team reduces by $2$ when two senior players aged $32$ and $30$ are replaced by $2$ youngsters of equal age. What is the age of these youngsters?

$A$ student finds the average of $10$ two-digit numbers. If the digits of one of the numbers are interchanged,the average increases by $3.6$. The difference between the digits of that two-digit number is: