Daily attendance (number of students) at a Ludhiana coaching centre over 60 days, recorded with inclusive classes:
21-25 -> 7, 26-30 -> 13, 31-35 -> 17, 36-40 -> 14, 41-45 -> 9.
After making the classes continuous, what are l and h for the median class?

Cumulative: 7, 20, 37, 51, 60, so $n=60$ and $\frac{n}{2}=30$. The first cf to reach 30 is 37, so the median class is 31-35. The gap between classes is $31-30=1$, so subtract 0.5 from the lower limit and add 0.5 to the upper: the continuous class is 30.5-35.5, giving $l=30.5$ and $h=35.5-30.5=5$. Taking $h=4$ from $35-31$ under-counts the class by one whole unit, and keeping $l=31$ skips the correction altogether.