The average monthly expenditure of a family for the first four months is $Rs.\, 2570$, for the next three months $Rs.\, 2490$ and for the last five months $Rs.\,3030.$ If the family saves $Rs.\, 5320$ during the whole $year,$ the average monthly income of the family during the year is (in $Rs.\,$) 

The average speed of a cyclist who covers first, second and third km at $20,16$ and $12\, km / hr$ respectively ( in $km / hr )$ is

The average revenue of $13$ consecutive years of a company $Rs.\, 70$ $\,lakhs.$ If the average of first $7 \,years$ is $Rs.\, 65$ $\,lakhs$ and that of last $7\, years$ is $Rs.\, 77$ $\,akhs,$ find the revenue for the $7^{th}$ $year.$ (Rs. in $lakh$)

A group of boys has an average weight of $36 \,kg$. One boy weighing $42 \,kg$ leaves the group and another boy weighing $30\, kg$ joints the group. If the average now becomes $35.7\, kg$, then how many boys are there in the group?

If the average of the ages of Rakesh and Mohan is $15,$ average of the ages of Mohan and Ramesh is $12$ and the average of the ages of Rakesh and Ramesh is $13,$ then the age of Mohan, is?