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 $?$

The mean of $100$ items was $46 .$ Later on, it was discovered that an item $16$ was misread as $61$ and another item $43$ was misread as $34.$ It was also found that the number of items was $90$ and not $100 .$ Then, what is the correct mean?

After replacing an old member by a new member, it was found that the average age of five members of a club is the same assit was $3 \,year$ ago. The difference between the ages of the replaced and the new member is ? (in $year$)

The average monthly salary of $20$ employees in an organisation is $Rs.\, 1500$. If the manager's salary is added, then the average salary increases by $Rs.\,100.$ What is the manager's monthly (in $Rs.$)

Average temperature of first $4 \,days$ of a week is $38.6^{\circ} C$ and that of the last $4\, days$ is $40.3^{\circ} C$. If the average temperature of the week be $39.1^{\circ} C$, the temperature on $4^{th}$ day is. (in $^{\circ} C$)

What was the average in $Rs.$ daily expenditure of a man in $1999$ who spent $Rs. \,6535$ in the first half year and $Rs.\, 88165$ in the last?