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Problem-Solving and Data AnalysisEasy–MediumInterval from an estimate and a margin

Problem-Solving and Data Analysis practice question

A poll of randomly selected voters estimates that 40% support a candidate, with a margin of error of 3 percentage points. Which of the following is the plausible range for the percentage of ALL voters who support the candidate?

  1. A. 37% to 43%Correct
  2. B. 40% to 43%
  3. C. 34% to 46%
  4. D. 37% to 40%

Answer: A. 37% to 43%

The margin of error extends 3 points on EACH side of the estimate: 40 − 3 = 37 up to 40 + 3 = 43.

Why the other answers are wrong

B. 40% to 43%
40% to 43% extends only upward; the true value could be below the estimate too.
C. 34% to 46%
34% to 46% uses 6 points each side, double the margin.
D. 37% to 40%
37% to 40% extends only downward.

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