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Explanation:

Analyze the relationship between confidence level and interval width

To determine which confidence level (\(90\%\), \(95\%\), or \(99\%\)) corresponds to each interval, we examine how the confidence level affects the width of a confidence interval.

A higher confidence level requires a larger critical value (e.g., \(z^*\) or \(t^*\)), which increases the margin of error:

$$ \text{Margin of Error} = \text{Critical Value} \times \text{Standard Error} $$

Since the sample size (\(n = 30\)) and sample standard deviation remain constant, a higher confidence level directly results in a wider confidence interval. Therefore:

  • The narrowest interval corresponds to the lowest confidence level (\(90\%\)).
  • The widest interval corresponds to the highest confidence level (\(99\%\)).
  • The intermediate interval corresponds to the middle confidence level (\(95\%\)).

Calculate the width of each given interval

Let's calculate the width (upper limit minus lower limit) for each of the three intervals:

  1. First Interval: Between \(7.3\) and \(8.7\) hours
$$ \text{Width} = 8.7 - 7.3 = 1.4 \text{ hours} $$
  1. Second Interval: Between \(7.0\) and \(9.0\) hours
$$ \text{Width} = 9.0 - 7.0 = 2.0 \text{ hours} $$
  1. Third Interval: Between \(7.2\) and \(8.8\) hours
$$ \text{Width} = 8.8 - 7.2 = 1.6 \text{ hours} $$

Match the intervals to their confidence levels

Now we rank the intervals by their widths and match them to the confidence levels (\(90\%\), \(95\%\), and \(99\%\)):

  • Narrowest interval: Width of \(1.4\) hours (Between \(7.3\) and \(8.7\) hours) matches the lowest confidence level, which is \(90\%\).
  • Intermediate interval: Width of \(1.6\) hours (Between \(7.2\) and \(8.8\) hours) matches the middle confidence level, which is \(95\%\).
  • Widest interval: Width of \(2.0\) hours (Between \(7.0\) and \(9.0\) hours) matches the highest confidence level, which is \(99\%\).

Answer:

Question 1

Between 7.3 and 8.7 hours of sleep: <blank>\(90\%\)</blank>

Question 2

Between 7.0 and 9.0 hours of sleep: <blank>\(99\%\)</blank>

Question 3

Between 7.2 and 8.8 hours of sleep: <blank>\(95\%\)</blank>