Q.Using the same daily-wages data as the previous example (0–20: 6, 20–40: 10, 40–60: 18, 60–80: 15, 80–100: 11 workers), calculate D6.

The decile class is found the same way as the quartile class, only the target position changes to iN/10. …

Step 1 — Locate the decile class. $k = \frac{6N}{10} = \frac{6(60)}{10} = 36$. From the cumulative frequencies (6, 16, 34, 49, 60), the first cf ≥ 36 is 49, in class 60–80 (L = 60, cf before = 34, f = 15, h = 20).

Step 2 — Interpolate. …

Cross-check via the equivalent percentile. D6 = P60 (Section 5). With $k=60(60)/100=36$ — the identical position — P60 must fall in the same 60–80 …

Re-using the SAME cumulative frequency total (N) computed for a different problem, rather than re-checking N for the dataset actually giv …