Chapter 20 estimating proportions with confidence


Answer: c Narrative: Bread machines



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Answer: c


Narrative: Bread machines

Suppose a survey was done this year to find out what percentage of all Americans own a bread machine. Out of their random sample of 1,000 Americans, 317 own a bread machine. The margin of error for this survey was plus or minus 3%.




  1. {Bread machine narrative} What proportion of the entire American population owns a bread machine, based on these results?

    1. Definitely 317/1,000 = .317 or 31.7%

    2. Probably between 28.7% and 34.7%

    3. 31.7% times the population of the U.S.

    4. None of the above.

Answer: b


  1. {Bread machine narrative} Suppose three years ago, 29% of Americans owned a bread machine. Based on the results of this current survey, what would you conclude (with high confidence) about the population of all Americans now compared with three years ago?

    1. A larger proportion of Americans own a bread machine now compared to three years ago.

    2. A smaller proportion of Americans own a bread machine now compared to three years ago.

    3. The proportion of Americans who own a bread machine has not significantly changed from three years ago.

    4. None of the above.

Answer: c


  1. Suppose the U.S. government reports that the total number of people in the U.S. who are currently infected with HIV is likely to be between 300,000 and 1,000,000. What is the margin of error for these findings? (Assume a symmetric 95% confidence interval.)

    1. +/ 350,000

    2. +/ 700,000

    3. +/ 5%

    4. Not enough information to tell



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