Question 20 • Concepts in Probability and Statistics A
Before the error, the scores in order were 80, 85, 90, 95, and 100. Their mean is 90, and the middle score—the median—is also 90, so A is true. Adding 0 creates an outlier; the new mean is 450 ÷ 6 = 75, and the new median is (85 + 90) ÷ 2 = 87.5, so C and E are true. The mean changed by 15 points, while the median changed by only 2.5 points, so F is true; the median did not remain the same.
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