The mean marks of $10$ boys in a class is $70 \%$,whereas the mean marks of $15$ girls is $60 \%$. The mean marks of all the $25$ students is

The average age of students of a class is $15.8 \text{ years}$. The average age of boys in the class is $16.4 \text{ years}$ and that of the girls is $15.4 \text{ years}$. The ratio of the number of boys to the number of girls in the class is:

The sum of three numbers is $98$. If the ratio between the first and second is $2:3$ and between the second and third is $5:8$,then the second number is:

The mean weight of $34$ students of a school is $42\, kg$. If the weight of the teacher is included, the mean weight increases by $400\, g$. Find the weight (in $kg$) of the teacher.

The average age of three boys is $15$ years. If the ratio of their ages is $3:5:7$,what is the age of the oldest boy in years?

The average of $12$ results is $15,$ and the average of the first two is $14.$ What is the average of the rest?