Answer: 3(Mean - Median)/SD.
- A (Mean - Mode)/SD
- B (Mean - Median)/SD
- C 3(Mean - Median)/SD
- D (Median - Mode)/SD
Correct answer: C. 3(Mean - Median)/SD
Explanation: Pearson's first skewness = (Mean - Mode)/SD. For grouped data the mode is ill-defined, so the second formula 3(Mean - Median)/SD is used instead via the empirical relation Mode ≈ 3Median - 2Mean. Answer: 3(Mean - Median)/SD.
In a perfectly normal (bell-shaped) distribution, mean, median, and mode all coincide at the centre; about 68% of data falls within 1 standard deviation of the mean, 95% within 2, and 99.7% within 3 - the empirical rule used to judge how typical or extreme a value is.
Concept context
Mean, median, mode, standard deviation, and data interpretation