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Question 864:

1. Suppose a 95% confidence interval for the mean daily sales for a sample of 100 days from an internet site is:($236, $318).
a. Will a 99% confidence interval for mean daily sales be wider or narrower than this?

2. Suppose a 95% confidence interval for the mean daily sales for a sample of 100 days from an internet site is: ($236, $318).
a. Will a 95% confidence interval for mean daily sales based on a sample of 50 days be wider or narrower than this?



3. Suppose we wish to conduct a survey of adult US voters about whether or not they intend to vote for an incumbent in congress in the next election. Suppose that we survey 1000 people and 230 say they will.
a. Calculate the margin of error for a 95% confidence interval for the true proportion who will vote for an incumbent. (Express your answer as a percentage.)

4. Suppose we have the same set-up as in the previous question, but we decide to question more people as we are not happy with the margin of error, and wish to reduce it to 2%.
a. Assuming the proportion of people who say yes in the sample remains at 23%, how many more people do we need to survey?

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