The average of $10$ numbers is $7$. What will be the new average if each of the numbers is multiplied by $8$?

In a school, the average age of students is $6 \, \text{years}$, and the average age of $12$ teachers is $40 \, \text{years}$. If the average age of the combined group of all the teachers and students is $7 \, \text{years}$, then the number of students is?

The average marks of a student obtained in Physics,Chemistry,and Biology is $70.$ If the student obtained $90$ marks in Mathematics,then the new average is

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

In an examination,out of $20$ students in a class,in Mathematics $2$ students scored $100$ marks,$3$ students scored $0$,and the average marks for the rest of the students was $40$. What is the average mark of the whole class? (in marks)

Average age of $15$ students of a class is $15 \text{ years}$. Out of these,the average age of $5$ students is $14 \text{ years}$ and that of the other $9$ students is $16 \text{ years}$. The age of the $15^{th}$ student is (in $\text{years}$):