$A, B, C$ and $D$ are four consecutive even numbers,respectively,and their average is $65$. What is the product of $A$ and $D$?

In a cricket team of $11$ boys,one player weighing $42 \,kg$ is injured and replaced by another player. If the average weight of the team is increased by $100 \,g$ as a result of this,then what is the weight of the new player (in $.1$)? (in $kg$)

The average of three numbers,of which the greatest is $16$,is $12$. If the smallest is half of the greatest,what is the remaining number?

Find the average of all prime numbers between $60$ and $90$.

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

The average of $X_{1}, X_{2}$ and $X_{3}$ is $14$. Twice the sum of $X_{2}$ and $X_{3}$ is $30$. What is the value of $X_{1}$?