Answer: 6.67.
- A 6.67
- B 10
- C 5
- D 8
Correct answer: A. 6.67
Explanation: Mean = 20. Deviations: |10-20|=10, |20-20|=0, |30-20|=10. Mean deviation = (10+0+10)/3 = 20/3 = 6.67.
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