Ans: (a) Least value $=0$, greatest value $=3$ (b) $4$
- The least possible value of the inter-quartile range $=0$.
The greatest possible value of the inter-quartile range $=3$.
- If $r=9$ and the median is $3$ hours, then the number of children having online hours less than or equal to 3 hours is $17$. Therefore, the number of children having online hours more than 3 hours must not greater than $16$.
$\therefore 0\le s \le 4$.
Therefore, there are $4$ possible values of $s$.
