The daily footfall (number of visitors) at 80 shops in a market is given as a 'more than' table:
more than 100 -> 80, more than 200 -> 68, more than 300 -> 47, more than 400 -> 25, more than 500 -> 9.
Find the median footfall.

Subtract each 'more than' entry from the one above it to get the ordinary frequencies: 12, 21, 22, 16, 9 for the classes 100-200, 200-300, 300-400, 400-500, 500-600 (total $n=80$). Now build the ordinary cumulative column: 12, 33, 55, 71, 80. With $\frac{n}{2}=40$ the first cf to reach 40 is 55, so the median class is 300-400 with $l=300$, cf = 33, $f=22,h=100$. Median = $300+\left(\frac{40-33}{22}\right)\times 100=300+31.82=331.82$ visitors. 231.82 uses cf = 55, the median class's own cumulative frequency. 333.33 uses $f=21$, the frequency of the preceding class. 300.32 drops the factor $h=100$.