A person travelled from one place to another at an average speed of $40 \,km / h$ and back to the original place at an average speed of $50\, km / h$. What is his average speed in $km / h$ during the entire trip?

The average age of $30$ girls is $1\, year.$ The average of first $18$ girls is $15\, year.$ Find out the average age of remaining $12$ girls?

The average marks in English subject of a class of $24$ students is $56 .$ If the marks of three students were misread as $44,45$ and $61$ of the actual marks $48,59$ and $67,$ respectively, then what would be the correct average?

A man retired from his service at the age of $60$ He served for $\frac{3}{5}^{ th}$ years of his retirement age. He joined his job at the age of (in $years$)

The average weight of $45$ students in a class is $52\, kg.$ Five of them whose average weight is $48 \,kg$ leave the class and other $5\, students$ whose average weight is $54\, kg$ join the class. What is the new average weight (in $kg$ ) of the class 

The average of $41$ consecutive odd numbers is $49 .$ What is the largest number.