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

$A$ cricketer had a certain average of runs for his $64$ innings. In his $65^{th}$ innings,he is bowled out for no score on his part. This brings down his average by $2$ runs. What is his new average of runs?

The average marks obtained by $180$ students in an examination is $50$. If the average marks of passed students is $80$ and the average marks of failed students is $40$,then what is the number of students who failed the examination?

The average age of $5$ sisters is $20 \, \text{years}$. If the age of the youngest sister is $4 \, \text{years}$,what was the average age of the group of sisters at the time of the birth of the youngest sister?

$A$ man travels by a car to his office at $60 \, km/h$ and returns home along the same route at $20 \, km/h$. Find the average speed of his whole journey (in $km/h$).

The frequency distribution data is given below. If the average age is $17 \text{ years}$,the value of $m$ is:

Age (in years)	$8, 20, 26, 29$
Number of People	$3, 2, m, 1$