Out of four numbers the average of the first three is $16$ and that of the last three is $15 .$ If the last number is $20$ then the first number is

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 $Rs.$)

The average weight of three boys $A, B$ and $C$ is $54 \frac{1}{3} \,kg,$ while the average weight of three boys $B , D$ and $E$ is $53 \,kg .$ What is the average weight of $A , B , C , D$ and $E$ ?(in $kg$)

The average age of a class of $30$ students and a teacher reduce by $0.5 \,years$ if we exclude the teacher. If the initial average is $14 \,years,$ find the age of the class teacher in $year$ ?

The average age of $11$ players of a cricket team is increased by $2 \,months$ when two of them aged $18\, years$ and $20 \,years$ are replaced by two new players. The average age of the new players is?

The mean marks of $10$ boys in a class is $70 \%$, whereas the mean marks of $15$ girls is $60 \%$. The mean marks of all the $25$ students is