An aeroplane travels $2500 \,km , 1200 \,km$ and $500\,km$ at $500\, km / h \,, 400 \,km $ and $250\,km / h $ respectively. The average speed is:(in $km/h$)

The average of nine numbers is $50.$ The average of the first five numbers is $54$ and that of the last three numbers is $52 .$ Then the sixth number is?

The average temperature from Monday to Thursday is $48^{\circ} C$ and from Tuesday to Friday, the average temperature is $52^{\circ} C$. If the temperature on Monday is $42^{\circ} C$, what was it on Friday in $^{\circ} C$?

The average age of $8$ men is increased by $2\,years$ when two of them whose ages are $21\, years$ and $23\, years$ are replaced by two new men. The average age of the two new men is

The average age of $8$ men is increased by $2\, years.$ When $2$ of them, whose ages are $20\, years$ and $24 \,years$ respectively, are replaced by $2$ women. What is the average age of these two women ? (in $years$)

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