The average of prime numbers between $1$ and $20$ is

$A$ 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?

The average of six numbers is $20$. If one number is removed,the average becomes $15$. What is the number removed?

The average age of $5$ members is $21 \text{ years}$. If the age of the youngest member is $5 \text{ years}$,find out the average age of the family at the birth of the youngest member (in $\text{years}$).

The average of $6$ numbers is $20$. If one number is removed, the average becomes $15$. What is the number removed?

The average of four consecutive odd numbers is $40$. What is the largest number?