The average of five consecutive odd integers is $27$. What is the product of the first and the last number?

The average weight of five persons sitting in a boat is $38\, kg$. The average weight of the boat and the persons sitting in the boat is $52\, kg$. What is the weight of the boat (in $kg$)?

$A$ car owner buys petrol at $Rs. 7.50$,$Rs. 8$,and $Rs. 8.50$ per litre for three successive years. What is the approximate average cost per litre of petrol if he spends $Rs. 4000$ each year?

$A$ man retired from his service at the age of $60$. He served for $\frac{3}{5}$ of his retirement age. At what age (in $years$) did he join his job?

The average salary of all the associates in a team is $Rs. 16000$. The average salary of $7$ senior associates is $Rs. 24000$ and the average salary of the rest is $Rs. 12000$. How many associates work in that team?

The arithmetic mean of $100$ observations is $24$. If $6$ is added to each of the observations and then each of them is multiplied by $2.5$,find the new arithmetic mean.