The $average$ of $30$ numbers is $12 .$ The $average$ of the first $20$ of them is $11$ and that of the next $9$ is $10 .$ The last number is

The average marks of a class of $35$ children is $35 .$ The marks of one of the students, who got $35,$ was incorrectly entered as $65 .$ What is the correct average of the class?

A cyclist goes from a place to another and returns by the same route. He pedals his way uniformly with speed $u$ while going and with speed $v$ while returning. The average speed of his journey 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 sum of three numbers is $98 .$ If the ratio between first and second be $2: 3$ and between second and third be $5: 8,$ then the second number is

In an examination the average marks was found to be $60.$ The marks of $80$ candidates had to be changed from $95$ to $70$ each and the average came down to $55$ marks. The total number of candidates attended the examination were