1990 AMC 8 Problem 20
Attempt Problem 20 of the 1990 AMC 8 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1990 AMC 8 solutions, or check the answer key.
All problems are used with official legal permission of the Mathematical Association of America (MAA).
20.
The annual incomes of families range from to In error, the largest income was entered on the computer as The difference between the mean of the incorrect data and the mean of the actual data is
Answer: A
Small hint:
Only one value changed, so only the total sum changes; the count stays at
Big hint:
Find how much the one wrong entry inflated the total, then divide that by
Solution:
Only one entry changed. The incorrect total exceeds the actual total by
Since this extra amount is spread over families, the means differ by
Thus, the correct answer is A .
Problem 20 in other years
- 1985 AMC 8
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