The average of prime numbers between $1$ and $20$ is
$9$
$9 \frac{5}{8}$
$10 \frac{1}{8}$
$8$
$16$ children are to be divided into two groups $A$ and $B$ of $10$ and $6$ children. The average percent marks obtained by the children of group $A$ is $75$ and the average per cent marks of all the $16$ children is $76 .$ What is the average per cent marks of children of group $B$ ?
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?
What will be the average of even numbers between $11$ to $63 ?$
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 mean marks of $10$ boys in a class is $70 \%$, whereas the mean marks of $15$ girls is $60 \%$. The mean marks of all the $25$ students is