The average age of students of a class is $15.8$ $years.$ The average age of boys in the class is $16.4\, years$ and that of the girls is $15.4 \,years.$ The ratio of the number of boys to the number of girls in the class is

The average of runs of a cricket player of $10$ innings was $32 .$ How many runs must he make in his next innings so as to increase his average of runs by $4 \,?$ 

The average temperature for Monday, Tuesday, Wednesday and Thursday was $48^{\circ}$. The average temperature for Tuesday, Wednesday, Thursday and Friday was $52^{\circ} .$ If the temperature on Monday was $42^{\circ} .$ then the temperature on Friday was (in $degrees$)

$16$ children are to be divided into two groups $A$ and $B$ of $10$ and $6$ children. The average percent marks obtained by the children of group $A$ is $75$ and the average per cent marks of all the $16$ children is $76 .$ What is the average per cent marks of children of group $B$ ?

The average of six numbers is $20 .$ If one number is removed, the average becomes $15 .$ What is the number removed ?

The average salary, per head, of all the workers of an institution is $Rs.\, 60 .$ The average salary of $12$ officers is $Rs.\, 400$; the average salary, per head, of the rest is $Rs.\,56.$ The total number of workers in the institution is