The average of four consecutive odd numbers is $40$. What is the largest number?

The average age of a family of $6$ members $4$ years ago was $25$ years. Meanwhile,a child was born in this family,and the average age of the whole family is still the same today. The present age of the child in years is?

The average of the squares of the first ten natural numbers is

The average of $8$ numbers is $20$. The average of the first two numbers is $15 \frac{1}{2}$ and that of the next three is $21 \frac{1}{3}$. If the sixth number is less than the seventh and eighth numbers by $4$ and $7$ respectively,then the eighth number is:

If the average of the ages of Rakesh and Mohan is $15$,the average of the ages of Mohan and Ramesh is $12$,and the average of the ages of Rakesh and Ramesh is $13$,then what is the age of Mohan?

The sum of the ages of father and son at present is $33 \, \text{years}$. Two years ago, the product of their ages was $28 \, \text{years}$. What is the age of the father and the son (in $\text{years}$)?