The average salary of $20$ workers in an office is $Rs.\, 1900$ per $month.$ If the manager's salary is added, the average becomes $Rs.\,2000$ per $month.$ The manager's annual salary (in $Rs.$) is

The average age of a group of persons going for a picnic is $16.75 \,years.$ $20$ new persons with an average age of $13.25 \,years$ join the group on the spot due to which the average of the group becomes $15\, years.$ Find the number of persons initially going for the picnic $?$

Five years ago, the average age of $P$ and $Q$ was $15 \,year.$ Now, average age of $P , Q$ and $R$ is $20 \,year.$ What whould be the age of $R$ after $10$ $year$ in $year$ ?

The average age of three boys is $15$ $year.$ If the ratio of their ages is $3:5: 7,$ what is the age of the oldest boy in $year$?

Average age of $5$ boys is $16$ $year$ of which that of $4$ boys is $16\, year\, 3\, months.$ The age of the $5^{th}$ boy is

A person travels $\frac{1}{3}$ of his journey by bus at $60\, km / h$ , $\frac{1}{3}$ by scooter at $30\, km / h$ and the rest by walking at $10 \,km / h$. Find his average speed for the whole journey. (in $km/h$)