Question

In a simple random sample of 90 cellphone owners, 67 own a smartphone.

1. Find the 85% confidence level for the percentage of all cellphone owners who own a smartphone, based on the sample data above. Give your answers as percentages to at least two decimal places. Do not type the percent signs.

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b. The margin of error for this confidence interval is   % (give your answer as a percentage to at least two decimal places).

A major credit card company wants to estimate the percentage of its cardholders have chosen the Personal Identification Number (PIN) of 1234 [which is a very bad idea, since it’s easy for someone to guess if your card is lost or stolen]. Specifically, the company will construct a 80% confidence interval for the true percentage of its cardholders who use this PIN, using a Simple Random Sample.

What is the critical value for such a confidence interval? Give your answer to exactly four decimal places.

Euniqua is considering running for political office, and wants to determine a 96% confidence interval for the true percentage of likely voters who will support her in the upcoming election. Assume she is able to use a Simple Random Sample from the population of likely voters.

What is the critical value for such a confidence interval? Give your answer to exactly four decimal places.

Answer 1

(a)

Answer: (67.82%, 81.06%)

(b)

The margin of error is 6.62%

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Critical value for 80% confidence interval:

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Critical value for 96% confidence interval:

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