The average age of a committee of $8$ members is $40 \text{ years}$. $A$ member,aged $55 \text{ years}$,retired and was replaced by a member aged $39 \text{ years}$. The average age of the present committee is (in $\text{years}$):

The average age of a group of persons going for a picnic is $16.75 \text{ years}$. $20$ new persons with an average age of $13.25 \text{ years}$ join the group on the spot,due to which the average age of the group becomes $15 \text{ years}$. Find the number of persons initially going for the picnic.

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 $\text{years}$)

On $24^{\text{th}}$ May,$2008$,the maximum temperatures of Delhi,Kolkata,and Mumbai were recorded as $35^{\circ}C$,$33^{\circ}C$,and $34^{\circ}C$ respectively. What was the maximum temperature of Chennai so that the average maximum temperature of those four cities would be $35^{\circ}C$ (in $^{\circ}C$)?

The average age of Seema,Sapna,Asha,Kavita,and Atrye is $40 \text{ years}$. The average age of Seema and Sapna is $35 \text{ years}$,and the average age of Asha and Kavita is $42 \text{ years}$. What is the age of Atrye?

What is the average of the squares of the first $19$ natural numbers?