The average of certain first consecutive natural numbers is $20.5$. Find their sum.

The average age of a husband and wife,who were married $7 \, \text{years}$ ago,was $25 \, \text{years}$ at the time of their marriage. Now,the average age of the family,including the husband,wife,and a child born during the interval,is $22 \, \text{years}$. What is the present age of the child in $\text{years}$?

The average of $7$ numbers is $5$. If the average of the first six of these numbers is $4$,the seventh number is:

If the average of $6$ consecutive even numbers is $25,$ the difference between the largest and the smallest number is

In a match,the average of runs scored by five players is $49$. If the runs scored by four players are $75, 30, 63,$ and $21$ respectively,then how many runs did the fifth player score?

What is the average of first $7$ multiples of $7$?