A group of boys has an average weight of $36 \,kg$. One boy weighing $42 \,kg$ leaves the group and another boy weighing $30\, kg$ joints the group. If the average now becomes $35.7\, kg$, then how many boys are there in the group?

Visitors to a show were charged $Rs.\, 15$ each on the first day, $Rs.\, 7.50$ on the second day, $Rs.\, 2.50$ on the third day and total attendance on three days were in the ratio $2: 5: 13$ respectively. The average charge per person for the entire three days is (in $Rs.$)

The average age of $30$ women decreases by $3$ $months$ if a new person Neha is included in place of a $25\, year$ old woman. Calculate the age of Neha in $year$ ?

Three years ago, the average age of a family of $5$ members was $17\, years.$ A baby having been born, the average age of the family is the same today. The present age of the baby is (in $years$)

The average of $7$ numbers is $5 .$ If the average of first six of these numbers is $4,$ the seventh number is

The sum of three numbers is $98 .$ If the ratio between first and second be $2: 3$ and between second and third be $5: 8,$ then the second number is