The average age of a class of $30$ students and a teacher reduce by $0.5 \,years$ if we exclude the teacher. If the initial average is $14 \,years,$ find the age of the class teacher in $year$ ?

In a family, the average age of a father and a mother is $35\, years.$ The average age of the father, mother and their only son is $27\, years.$ What is the age of the son ? (in $years$)

A person covers $9\, km$ with a speed of $3 \,km / h , 25 \,km$ with a speed of $5\, km / h$ and $30\, km$ with a speed of $10\, km / h$. Find out the average speed of person in $km / h$ ?

If the average of $x$ and $\frac{1}{x}(x \neq 0)$ is $M,$ then the average of $x^{2}$ and $\frac{1}{x^{2}}$ is

The average marks of $40$ students in an English exam is $72 .$ Later it is found that three marks $64 , 62$ and $84$ were wrongly entered as $68,65$ and $73.$ The average after mistakes were rectified is

In a $20$ over match, the required run rate to win is $7.2 .$ If the run rate is $6$ at the end of the $15^{th}$ over, the required run rate to win the match is