- AThe cf of the median class itself was used instead of the cf of the class before it
- BThe wrong class width h was used
- CThe modal class was used in place of the median class
- Dn was not halved before being put into the formula
Step-by-Step Solution
n = 50 and n/2 = 25; the cumulative frequencies are 8, 20, 40, 50, so the median class 20–30 is right. But cf in the formula is the cumulative frequency of the class BEFORE the median class, which is 20 — not 40. The correct value is 20 + 10(25 − 20)/20 = 22.5. A negative bracket is the tell-tale sign of this slip.
Answer: A) The cf of the median class itself was used instead of the cf of the class before it