Average age of $A, B$ and $C$ is $84\, years.$ When $D$ joins them the average age becomes $80\, years.$ A new person, $E,$ whose age is $4 \,years$ more than $D,$ replaces $A$ and the average of $B, C, D$ and $E$ becomes $78\, years.$ What is the age of $A$ ? (in $years$)

A man whose bowling average is $12.4,$ takes $5$ wickets for $26$ runs and, thereby, decreases his average by $0.4$ The number of wickets, taken by him, before his last match is

$16$ children are to be divided into two groups $A$ and $B$ of $10$ and $6$ children, respectively. The average marks obtained by the children of group $A$ is $75$ and that of all the children is $76 .$ Then, the average marks of the children of group $B$ is ?

Average weight of $3 \,cm$ men $A , B , C$ is $84 \,kg$. Another man $D$ joins the group and the average now becomes $80 \,kg$. If another man $E$ whose weight is $3 \,kg$ more than that of $D$ replaces $A$ then the averageweight of $B , C , D$ and $E$ becomes $79\, kg .$ The weight of $A$ in $kg$ is

The average annual income (in $Rs.$) of certain agricultural workers is $S$ and that of other workers is $T$. The number of agricultural workers is $11$ times that of other workers. Then the average annual income (in $Rs.$) of all the workers is

The average of $6$ observations is $12 .$ A new seventh observation is included and the new average is decreased by $1$. The seventh observation is