Answer: 24.
- A 25
- B 24
- C 26
- D 22
Correct answer: B. 24
Explanation: Combined mean = (20·30 + 30·20)/50 = 1200/50 = 24.
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