The average age of students of a class is $15.8 \, \text{years}$. The average age of boys in the class is $16.4 \, \text{years}$ and that of the girls is $15.4 \, \text{years}$. The ratio of the number of boys to the number of girls in the class is:

$16$ 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 percent marks of all the $16$ children is $76$. What is the average percent marks of children of group $B$?

The average speed of a cyclist who covers the first,second,and third km at $20, 16,$ and $12 \, km/hr$ respectively (in $km/hr$) is:

The arithmetic mean of the scores of a group of students in a test was $52$. The brightest $20\%$ of them secured a mean score of $80$ and the dullest $25\%$ a mean score of $31$. The mean score of the remaining $55\%$ is

If the average of $m$ numbers is $n^{2}$ and that of $n$ numbers is $m^{2},$ then the average of $(m + n)$ numbers is

The average weight of $A, B$ and $C$ is $84 \, kg$. If $D$ joins,the average weight now is $80 \, kg$. If another person $E$,who is $3 \, kg$ heavier than $D$,replaces $A$,then the average weight of $B, C, D$ and $E$ becomes $79 \, kg$. What is the weight of $A$ in $kg$?