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 ?

Out of three numbers, the first is twice the second and is half of the third. If the average of the three numbers is $56,$ the three numbers in order are

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 $kg$ ?

$10$ $years$ ago the average age of all the $25$ $teachers$ of the Girls college was $45\, years.$ $4 \,years$ ago, the principal has retired from her post at the age of $60 \,year.$ So after one year a new principal whose age was $54 \,years$ recruited from outside. The present average age of all the teachers is, if principal is also considered as a teacher

The average age of a family of $6$ members is $22\, years.$ If the age of the youngest member be $7\, years,$ then what was the average age of the family at the birth of the youngest member?

Find the average of first $25$ multiples of $5 .$