The average of certain first consecutive natural numbers is $20.5$. Find their sum.

The average of $10$ numbers is $7$. What will be the new average if each of the numbers is multiplied by $8$?

The total marks obtained by a student in Physics,Chemistry and Mathematics together is $120$ more than the marks obtained by him in Chemistry. What is the average marks obtained by him in Physics and Mathematics together?

The average of $7$ numbers is $5$. If the average of the first six of these numbers is $4$,the seventh number is:

$3 \, \text{years}$ ago,the average age of a family of $5 \, \text{members}$ was $17 \, \text{years}$. With the birth of a new baby,the average age of the $6 \, \text{members}$ remains the same even today. Find the age of the new baby in years.

What was the average daily expenditure in $Rs.$ of a man in $1999$ who spent $Rs. \, 76535$ in the first half of the year and $Rs. \, 88165$ in the second half?