The mean weight of $150$ students in a class is $60 \, kg$. The mean weight of boys is $70 \, kg$ and that of girls is $55 \, kg$. What is the number of boys in the class?

The average age of $5$ boys is $16$ years, of which the average age of $4$ boys is $16$ years $3$ months. The age of the $5^{th}$ boy is:

The average age of Donald,his wife,and their two children is $23 \text{ years}$. His wife is $4 \text{ years}$ younger than Donald,and his wife was $24 \text{ years}$ old when his daughter was born. He was $32 \text{ years}$ old when his son was born. What is the average age of Donald and his daughter? (in $\text{years}$)

The average of five numbers is $27$. If one number is excluded,the average becomes $25$. The excluded number is

The average of ten numbers is calculated. If each number is increased by $12 \%$,then the average

What will be the average of even numbers between $11$ and $63$?