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 $\text{years}$).

$A$ family consists of grandparents,parents,and three grandchildren. The average age of the grandparents is $67 \text{ years}$,that of the parents is $35 \text{ years}$,and that of the grandchildren is $6 \text{ years}$. What is the average age of the family? (in $\text{years}$)

The sum of three consecutive odd numbers is $38$ more than the average of these numbers. What is the first of these numbers?

$A$ motorist covered the first $20 \text{ km}$ of his journey in $30 \text{ minutes}$ and the remaining $29 \text{ km}$ in $40 \text{ minutes}$. His average speed in $\text{km/hr}$ is:

The average salary per head of all the workers in a workshop is $Rs. 850$. If the average salary per head of $7$ technicians is $Rs. 1000$ and the average salary per head of the rest is $Rs. 780$,find out the total number of workers in the workshop.