The average salary of $15$ persons is $Rs. 5,500$. If the salary of one person is added,the average increases to $Rs. 5,700$. What is the salary of this one person in $Rs.$?

The average of $7$ consecutive numbers is $20$. The largest of these numbers is

There are $6$ consecutive odd numbers in increasing order. The difference between the average of the squares of the first $4$ numbers and the last $4$ numbers is $64$. If the sum of the squares of the first and the last element is $178$,then the average of all the $6$ numbers is:

$10$ years ago,the average age of a family of $4$ members was $24$ years. Two children have been born (with an age difference of $2$ years),and the present average age of the family remains the same. The present age of the youngest child is (in years):

$A$ person travels $\frac{1}{3}$ of his journey by bus at $60\, km/h$,$\frac{1}{3}$ by scooter at $30\, km/h$,and the rest by walking at $10\, km/h$. Find his average speed for the whole journey (in $km/h$).

The average of $11$ numbers is $10.9$. If the average of the first six is $10.5$ and the average of the last six is $11.4$, find the middle (sixth) number.