What is the average of first $7$ multiples of $7$?

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

The average weight of $A, B$ and $C$ is $45\, kg$. If the average weight of $A$ and $B$ is $40\, kg$ and that of $B$ and $C$ is $43\, kg$,then the weight of $B$ is (in $, kg$)

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 $kg$).

$A$ 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 marks of Sameer decreased by $1,$ when he replaced the subject in which he scored $40$ marks with two other subjects in which he scored $23$ and $25$ marks respectively. Later,he also included $57$ marks of Computer Science,and the average marks increased by $2.$ How many subjects were there initially?