The average of marks obtained by $120$ candidates in a certain examination is $35$. If the average marks obtained by passed candidates are $39$ and those of the failed candidates are $15$,then what is the number of candidates who passed the examination?

The average age of a group of persons going for a picnic is $16.75 \text{ years}$. $20$ new persons with an average age of $13.25 \text{ years}$ join the group on the spot,due to which the average age of the group becomes $15 \text{ years}$. Find the number of persons initially going for the picnic.

The average age of $A, B, C, D$ five years ago was $45$ years. By including $x$,the present average age of all the five is $49$ years. The present age of $x$ is (in years):

The average salary per head of all the workers in a company is $Rs. \,95$. The average salary of $15$ officers is $Rs. \,525$ and the average salary per head of the rest is $Rs. \,85$. Find the total number of workers in the workshop.

$A$ club has $15$ men and $25$ women. The average age of men is $10 \text{ years}$ and the average age of women is $12 \text{ years}$. What is the average age of the whole club in years?

The average of $13$ results is $60$. If the average of the first $7$ results is $59$ and that of the last $7$ results is $61$,what will be the seventh result?