The average of nine numbers is $50$. The average of the first five numbers is $54$ and that of the last three numbers is $52$. Then the sixth number is?

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

The average age of $20$ boys in the class is $15.6$ years. Five new boys join and the new average becomes $15.56$ years. What is the average age of the five new boys (in years)?

The average age of a class of $30$ students and a teacher reduces by $0.5 \, \text{years}$ if we exclude the teacher. If the initial average is $14 \, \text{years}$,find the age of the class teacher in $\text{years}$.

The average weight of three boys $A, B$ and $C$ is $54 \frac{1}{3} \, kg,$ while the average weight of three boys $B, D$ and $E$ is $53 \, kg.$ What is the average weight of $A, B, C, D$ and $E$ (in $kg$)?

The average of $6$ numbers is $8$. What is the $7^{th}$ number so that the average becomes $10$?