The duration (in minutes) of 120 calls handled at a Nashik call centre:
0-4 -> 18, 4-8 -> 26, 8-12 -> 32, 12-16 -> 28, 16-20 -> 16.
Find the median call duration (minutes).

Cumulative: 18, 44, 76, 104, 120, so $n=120$ and $\frac{n}{2}=60$. The first cf to reach 60 is 76, so the median class is 8-12 with $l=8$, cf = 44, $f=32,h=4$. Median = $8+\left(\frac{60-44}{32}\right)\times 4=8+\frac{1}{2}\times 4=10$ minutes. 8.5 forgets to multiply by $h=4$ (it adds only the fraction $\frac{1}{2}$). 6 uses cf = 76, the cumulative frequency of the median class itself. 10.46 uses $f=26$, the frequency of the preceding class.