Ten years ago,the average age of $P$ and $Q$ was $20 \text{ years}$. The average age of $P, Q,$ and $R$ is $30 \text{ years}$ now. After $10 \text{ years}$,the age of $R$ will be (in $\text{years}$):

The average weight of $3$ persons is $65 \, kg$. If a fourth person having a weight of $45 \, kg$ joins the group,what is the average weight of the group? (in $kg$)

The average of $20$ numbers is $30$ and that of other $30$ numbers is $50$. What is the average of all the numbers?

Visitors to a show were charged $Rs. 15.00$ each on the first day,$Rs. 7.50$ on the second,and $Rs. 2.50$ on the third day. The total attendance of visitors for the three days was in the ratio $2:5:13$. Find the average charge per visitor for the entire show (in $Rs.$).

The average of $50$ numbers is $38$. If two numbers $45$ and $55$ are discarded,the average of the remaining set of numbers is:

$A$ batch of $60$ students made an average score of $50$ marks and another batch of $40$ students made an average score of $45$ marks. What is the overall average score?