The weights (in grams) of 150 tomatoes graded at a mandi:
40-60 -> 22, 60-80 -> 31, 80-100 -> 42, 100-120 -> 33, 120-140 -> 22.
Find the median weight (g).

Cumulative: 22, 53, 95, 128, 150, so $n=150$ and $\frac{n}{2}=75$. The first cf to reach 75 is 95, giving median class 80-100 with $l=80$, cf = 53, $f=42,h=20$. Median = $80+\left(\frac{75-53}{42}\right)\times 20=80+\frac{440}{42}=90.48$ g. 70.48 uses cf = 95, the median class's own cumulative frequency, which makes the correction negative. 80.52 leaves out the factor $h=20$. 94.19 uses $f=31$, the frequency of the class before the median class.