The average marks obtained by $150$ students in an examination is $40$. If the average marks of passed students is $60$ and that of the failed students is $20$,what is the number of students who passed the examination?

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

$A$ batsman scores $98$ runs in the $17^{\text{th}}$ match of his career. His average runs per match increases by $2.5$. What is his average before the $17^{\text{th}}$ match?

In a class,the average height of all students is $a \text{ cm}$. Among them,the average height of $10$ students is $b \text{ cm}$ and the average height of the remaining students is $c \text{ cm}$. Find the number of students in the class. (Here $a > c$ and $b > c$)

The average expenditure of a man for the first five months is $Rs.\, 3600$ and for the next seven months it is $Rs.\, 3900$. If he saves $Rs.\, 8700$ during the year,his average income per month is (in $Rs.$)

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 $kg$?