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Cogito

AP Statistics · Chapter 3 · Lesson 1

Practice Worksheet

Confidence Intervals for a Proportion

An estimate with its uncertainty attached.

11 problems · about 25 minutes · AP Statistics 6.1, 6.3

NameDate

Figure — use these to answer the problems

An interval covers a stretch of the line, not a single point.
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5

The estimate5
Figure 1

Warm Up

Straightforward practice. Get the method working first.

4 problems

  1. Estimate 55%, margin 6%. Lower end as a percent?

    Answer

  2. Estimate 40%, margin 5%. Lower end as a percent?

    Answer

  3. Estimate 40%, margin 5%. Width of the interval, in percentage points?

    Answer

  4. A larger sample makes the interval which? 1 for narrower, 2 for wider.

    Answer

Build It Up

The same ideas with more to keep track of.

3 problems

  1. Raising confidence from 95% to 99% makes it which? 1 for narrower, 2 for wider.

    Answer

  2. Select every correct interpretation of a 95% confidence interval.

    • The method captures the true value in 95% of samples.
    • There is a 95% chance the true value is in this interval.
    • The true value is fixed; the interval varies.
    • 95% of the data lies in the interval.
    • Tick every box that applies.

  3. Interval 49% to 55%. Does it establish a majority? 1 for yes, 0 for no.

    Answer

Stretch Yourself

Mixed problems. Work out what kind of question it is before you start.

4 problems

  1. Estimate 70%, margin 2%. Upper end as a percent?

    Answer

  2. To halve the margin of error, roughly how many times the sample size is needed?

    Answer

  3. The Lower End

    Estimate 60% with margin of error 4%. What is the lower end, as a percent?

    Answer

  4. The Upper End

    Same interval. What is the upper end, as a percent?

    Answer