AP Statistics · Topic 7.3

Justifying a Claim About a Population Mean Based on a Confidence Interval Practice

Part of Inference for Quantitative Data: Means.(UNC-4.F)

Practice questions

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Sample questions

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  1. Sample 1difficulty 1/5

    A 90% confidence interval for the mean weight of adult salmon is (4.2, 4.8) kg.

    4.2 4.8 90% CI for mu (kg)

    Which is a correct interpretation?

    • A

      We are 90% confident the population mean weight is between 4.2 and 4.8 kg.

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    • B

      90% of samples will have a mean between 4.2 and 4.8 kg.

    • C

      There is a 90% probability that the true mean is in this interval.

    • D

      90% of adult salmon weigh between 4.2 and 4.8 kg.

    Why

    A confidence interval describes our confidence in capturing the population parameter, not individual values, probability, or future samples.

  2. Sample 2difficulty 1/5

    A statistician constructs many 95% confidence intervals for a population mean using independent random samples.

    mu repeated 95% CIs

    Which statement best describes the meaning of "95% confidence"?

    • A

      The probability that any one interval contains the mean is 0.95.

    • B

      The sample mean lies in 95% of intervals.

    • C

      About 95% of such intervals would capture the true population mean.

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    • D

      95% of the data will fall within the interval.

    Why

    Confidence level refers to the long-run capture rate of the procedure across repeated samples.

  3. Sample 3difficulty 3/5

    "We are 90% confident that μ is between 50 and 56" interprets a

    • A

      Mean

    • B

      90% CI

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    • C

      Type I error

    • D

      Significance level

    Why

    Standard CI interpretation.

  4. Sample 4difficulty 3/5

    A 95% CI for mean reaction time of (240, 280) ms means

    • A

      Mean is exactly 260 ms

    • B

      95% of subjects respond between 240–280 ms

    • C

      Reaction times average 95% accurate

    • D

      We are 95% confident mean reaction time is between 240 and 280 ms

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    Why

    CI describes the parameter, not individual values.

  5. Sample 5difficulty 3/5

    A 95% CI for μ is computed as (10.5, 13.5). The point estimate is

    • A

      1.5

    • B

      10.5

    • C

      12.0

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    • D

      13.5

    Why

    Midpoint = (10.5 + 13.5)/2 = 12.0.