$A$ student bought $4$ books for $Rs. 120$ from one book shop and $6$ books for $Rs. 150$ from another. The average price (in rupees),he paid per book was

The average age of $80$ boys in a class is $15.$ The average age of a group of $15$ boys in the class is $16$ and the average age of another $25$ boys in the class is $14.$ What is the average age of the remaining boys in the class?

$16$ children are to be divided into two groups $A$ and $B$ of $10$ and $6$ children,respectively. The average marks obtained by the children of group $A$ is $75$ and that of all the children is $76$. Then,the average marks of the children of group $B$ 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 a group of $15$ students is $10 \, \text{years}$. When $5$ more students joined the group,the average age increased by $1 \, \text{year}$. If the average age of the $5$ new students is $x$,find the value of $x$ (in $\text{years}$).

The average of $5$ quantities is $6$. The average of three of them is $8$. What is the average of the remaining two quantities?