The cost of $5 \,kg$ of apples is $Rs.\, 450 .$ The cost of $12$ dozen mangoes is $Rs.\, 4320$, and the cost of $4 \,kg$ of oranges is $Rs.\,240.$ What is the total cost of $8 \,kg$ of apples$, 8$ dozens of mangoes and $8 \,kg$ of oranges ? (in $Rs.$)

$16$ children are to be divided into two groups $A$ and $B$ of $10$ and $6$ children. The average percent marks obtained by the children of group $A$ is $75$ and the average per cent marks of all the $16$ children is $76 .$ What is the average per cent marks of children of group $B$ ?

$3 \,years$ ago the average age of a family of $5 \,members$ was $17 \,years,$ with the birth of a new baby, the average age of six members remains the same even today. Find the age of the new baby in $year$.

The average weight of $15$ oarsmen in a boat is increased by $1.6\, kg$ when one of the crew, who weighs $42\, kg$ is replaced by a new man. Find the weight of the new man (in $kg$)

The average of first nine prime numbers is