If the average marks of three batches of $55, 60,$ and $45$ students are $50, 55,$ and $60$ respectively,then the average marks of all the students is:

In a school with $600$ students,the average age of the boys is $12$ $years$ and that of the girls is $11$ $years$. If the average age of the school is $11$ $years$ and $9$ $months$,then the number of girls in the school is:

The average of $100$ observations was calculated as $35$. It was found later that one of the observations was misread as $83$ instead of $53$. The correct average is: (in $.7$)

The average age of $80$ boys in a class is $15.$ The average age of a group of $15$ boys in the class is $16$ and the average age of another $25$ boys in the class is $14.$ What is the average age of the remaining boys in the class?

The average weight of $A, B$ and $C$ is $45\, kg$. If the average weight of $A$ and $B$ is $40\, kg$ and that of $B$ and $C$ is $43\, kg$,then the weight of $B$ is (in $, kg$)

The average value of the numbers $15, 21, 32, 35, 46, x, 59, 65, 72$ should be greater than or equal to $43$ but less than or equal to $44$. Then the value of $x$ should be