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

The average weight of $36$ students is $50 \,kg$. It was found later that the figure of $37 \,kg$ was misread as $73 \,kg.$ What is the correct average? (in $kg$)

The average weight of a group of $20$ boys was calculated to be $89.4 kg$ and it was later discovered that one weight was misread as $78 kg$ instead of the correct one of $87 kg$. The correct average weight is in $kg$

The average monthly income of $P$ and $Q$ is $Rs.\,5050.$ The average monthly income of $Q$ and $R$ is $Rs.\,6250$ and the average monthly income of $P$ and $R$ is $Rs.\,5200.$ The monthly income of $P$ is

A student finds the average of $10,2$ digit numbers. If the digits of one of the number is interchanged, the average increases by $3.6 .$ The difference between the digits of the $2 -$digit numbers is