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):

If the average marks of three batches of $55, 60,$ and $45$ students are $50, 55,$ and $60$ respectively,then the average marks of all the students is:

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

The average of ten numbers is calculated. If each number is increased by $12 \%$,then the average

$A$ batsman in his $17^{th}$ innings makes a score of $85$ runs,and thereby,increases his average by $3$ runs. What is his average after the $17^{th}$ innings? He had never been 'not out'.

The average of runs scored by a cricketer in his $99$ innings is $99$. How many runs will he have to score in his $100^{\text{th}}$ innings so that his average of runs in $100$ innings may be $100$?