The average age of a committee of $8$ members is $40 \text{ years}$. $A$ member,aged $55 \text{ years}$,retired and was replaced by a member aged $39 \text{ years}$. The average age of the present committee is (in $\text{years}$):

Last year,$5$ companies had an average of $16$ non-working days each. If $3$ companies had $16$ non-working days each and $2$ companies had $5$ fewer non-working days each,what was the average number of non-working days for these $5$ companies last year?

The average weight of $10$ students is increased by $0.5 \, kg$ when one of the students weighing $50 \, kg$ is replaced by a new student. Find the weight of the new student (in $kg$).

The average of $30$ numbers is $15$. The average of the first $18$ numbers is $10$ and that of the next $11$ numbers is $20$. The last number is:

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

The batting average of a cricket player for $64$ innings is $62$ runs. His highest score exceeds his lowest score by $180$ runs. Excluding these two innings,the average of the remaining innings becomes $60$ runs. His highest score was (in $Runs$):