The average age of $8$ men is increased by $2\, \text{years}$ when two of them whose ages are $21\, \text{years}$ and $23\, \text{years}$ are replaced by two new men. The average age of the two new men is:

In a class,the average height of all students is $a \text{ cm}$. Among them,the average height of $10$ students is $b \text{ cm}$ and the average height of the remaining students is $c \text{ cm}$. Find the number of students in the class. (Here $a > c$ and $b > c$)

What is the age of a class teacher?
$I.$ There are $11$ students in the class.
$II.$ The average age of the students and the teacher is $14$ years.
$III.$ The average age of the teacher and the students is $3$ years more than that of the students.

The average of prime numbers between $1$ and $20$ is

Find the average of the following set of scores: $253, 124, 255, 534, 836, 375, 101, 443, 760$.

The average weight of $3$ men $A, B$ and $C$ is $84 \, kg$. Another man $D$ joins the group and the average now becomes $80 \, kg$. If another man $E$,whose weight is $3 \, kg$ more than that of $D$,replaces $A$,then the average weight of $B, C, D$ and $E$ becomes $79 \, kg$. The weight of $A$ is (in $kg$)