1. Question: In a random sample of 350 attendees of a minor league baseball game, 184 said that they bought food from the concession stand. Create a 95% confidence interval for the proportion of fans who bought food from the concession stand. Use Excel to create the confidence interval, rounding to...
Week 6 Assignment: Understanding Confidence Intervals - Excel
Calculate a Confidence Interval for a Proportion - Excel
Question
In a random sample of 350 attendees of a minor league baseball game, 184 said
that they bought food from the concession stand. Create a 95% confidence
interval for the proportion of fans who bought food from the concession stand. Use
Excel to create the confidence interval, rounding to four decimal places.
Yes that's right. Keep it up!
(0.4734, 0.5780)
Answer Explanation
Correct answers:
0.4734
0.5780
The confidence interval for the unknown population
proportion p is (p̂ −z⋆p̂ (1−p̂ )n‾‾‾‾‾‾‾‾‾√,p̂ −z⋆p̂ (1−p̂ )n‾‾‾‾‾‾‾‾
‾√). The confidence interval can be calculated using Excel.
1. Identify α. Click on cell A1 and enter =1−0.95 and press ENTER.
2. Thus, α=0.05. Enter the number of successes, x=184, and sample
size, n=350, in the Excel sheet in cells A2 and A3. To find the proportion of
successes, p̂ , click on cell A4 and enter =A2/A3 and press ENTER.
3. Thus, p̂ ≈0.5257. Use the NORM.S.INV function in Excel to find z⋆. Click on
cell A5, enter =NORM.S.INV(1−A1/2), and press ENTER.
4. The answer for z⋆, rounded to two decimal places, is z⋆≈1.96. To calculate the
standard error, p̂ (1−p̂ )n‾‾‾‾‾‾‾‾‾√, click on cell A6 and
enter =SQRT(A4∗(1−A4)/A3) and press ENTER.
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