The average weight of $100$ students is $32\, kg$. The average weight of first $49$ students is $30\, kg$ and that of last $50$ students is $34\, kg$. What is the weight (in $kg$ ) of the $50^{ th }$ student ?

The average age of $5$ members is $21 \,years.$ If the age of the youngest member be $5 \,years,$ find out the average age of the family at the birth of the youngest member.(in $years$)

The average pocket-money of $3$ friends $A, B, C$ is $Rs.\, 80$ $month.$ If $B$ spends double and $C$ spends triple of whate $A$ spends during that month and if the average of their unspent pocketemoney is $Rs.$ $60,$ then $A$ spends (in $Rs.$)

The average weight of $3$ person is $65 \,kg$. If a fourth person having a weight of $45 \,kg$ joins the group, what is the average weight of the group ? (in $kg$)

A library has an average of $510$ $visitors$ on Sundays and $240$ on other days. The average number of visitors per day in a month of $30 \,days$ beginning with a Sunday is 

Five years ago the average age of husband and wife was $23\, years.$ Today the average age of husband, wife and child is $20 \,years.$ How old is child in $years$ ?