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?

The average of $13$ results is $50 .$ If the average of first $7$ results is $52$ and that of last $7$ results is $49,$ find the $7^{th}$ result.

The average salary per head of all the workers in a workshop is $Rs.\,850.$ If the average salary per head of $7$ technicians is $Rs.\, 1000$ and the average salary per head of the rest is $Rs.\, 780,$ find out the total number of workers in the workshop.

The average weight of $24$ students is $35\, kgs.$ If the weight of teacher is added the average increased by $400\, gms$. What is the weight of the teacher? (in $kg$)

The average age of a graph of $9$ students is $20\, years.$ When $6$ more students joined the group, the average age falls by $2\, years.$ Then the average age of new students is

The average of first $25$ numbers is $10$ and the average of the next $25$ numbers is $12 .$ The average of all $50$ numbers is