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

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:

Mr. Patel walked $6 \, km$ to reach the station from his house,then he boarded a train whose average speed was $60 \, km/hr$ and thus he reached his destination. In this way,he took a total of $3 \, hours$. If the average speed of the entire journey was $32 \, km/hr$,then the average speed of walking is (in $km/hr$):

The average of the first $46$ natural numbers is:

Find the average of first $25$ multiples of $5$.

$A, B, C$ and $D$ are four consecutive even numbers,respectively,and their average is $65$. What is the product of $A$ and $D$?