SAT Math Multiple Choice Question 361: Answer and Explanation

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Question: 361

1. The U.S. Centers for Disease Control recommends that adults engage in 2.5 hours per week of vigorous exercise. A local health society conducts a survey to see if people are meeting this goal. They ask 100 people with gym memberships how many minutes of exercise they engage in per week. After analyzing the data, the health society finds that the average respondent exercises 142 minutes per week, but the margin of error was approximately 36 minutes. The society wants to lower this margin of error. Using which of the following samples instead would do so?

  • A. 50 people with gym memberships
  • B. 50 people randomly selected from the entire adult population
  • C. 100 people with gym memberships, but from a variety of gyms
  • D. 200 people randomly selected from the entire adult population

Correct Answer: D



Difficulty: Easy

Category: Problem Solving and Data Analysis / Statistics and Probability

Strategic Advice: A larger sample size is always likely to result in a lower margin of error, so you can immediately eliminate A and B.

Getting to the Answer: To reduce the margin of error, the society should use a larger sample size selected from a better representation of the population. The target population is all adults, not just those that have gym memberships. Using only adults with gym memberships is likely to skew the results because these respondents probably exercise considerably more than people who do not have gym memberships. This means (D) is correct.

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