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

The average age of board of directors of a company, having $10$ directors was $48$ years. Coincidentally when a director aged $53$ resigned from the board of directors, another director died on the same day. So a new director joined the board of directors aged $34.$ Next year in the same month the average age of all the $9$ directors was found to be $46 \,years.$ The age of the late (i.e., dead) director at the time of his death was (in $years$)

$16$ 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 ?

The average of $50$ numbers is $38 .$ If two numbers, namely, $45$ and $55$ are discarded, what is the average of the remaining numbers ?

The average speed of a train running at a speed of $30\, km / h$ during the first $100\, kilometres,$ at $40\, km / h$ during the second $100\, kilometres$ and at $50\,km / h$ during the last $100\, kilometres$ is nearly (in $km/h$)

The average of certain first consecutive even number is $101.$ Find their sum?