The average weight of $10$ students is increased by $0.5 \, kg$ when one of the students weighing $50 \, kg$ is replaced by a new student. Find the weight of the new student (in $kg$).

What is the average of the squares of the first $19$ natural numbers?

The average of $3$ consecutive numbers is $n$. If the next two consecutive numbers are also included,the average of the five numbers will

In a class of $100$ students,the mean marks obtained in a subject is $30$ and in another class of $50$ students the mean marks obtained in the same subject is $60$. The mean marks obtained by the students of two classes taken together is

There are three baskets of fruits. The $1^{st}$ basket has twice the number of fruits in the $2^{nd}$ basket. The $3^{rd}$ basket has three-fourths of the fruits in the first. The average of the fruits in all the baskets is $30$. What is the number of fruits in the first basket?

$A$ car owner buys petrol at $Rs. 7.50$,$Rs. 8$,and $Rs. 8.50$ per litre for three successive years. What is the approximate average cost per litre of petrol if he spends $Rs. 4000$ each year?