In a school, the average age of students is $6 \,years$ , and the average age of $12$ teachers is $40\, years.$ If the average age of the combined group of all the teachers and students is $7 \,years$ , then the number of students is?

The arithmetic mean of the following numbers is $1,2,2,3,3,3,4,4,4,4,5,5,5,5,5,6,6,6,6,6,6,7,7,7,7,7,7,7$

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 $4 \,?$ 

Last year, $5$ companies had an average of $16$ non working days each, and $2$ companies had $5$ fewer non working days each. What was the average number of non working days given by the same companies this $year$ ?

The average expenditure of a man for the first five months is $Rs.\, 120$ and for the next seven months is $Rs. \,130$ . His monthly average income in $Rs.$ if he saves $Rs. \,290$ in that year, is

Average age of $15$ students of a class is $15\, years.$ Out of these the average age of $5$ students is $14 \,years$ and that of the other $9$ students is $16\, years.$ The age of the $15^{th}$ student is (in $years$)