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# Confidence Interval & Sample size

An election poll reported that a candidate had an approval rating of 48% with a margin of error E of 3%. Construct a confidence interval for the proportion of adults who approve of the candidate.

You are a travel agent and wish to estimate, with 95% confidence, the proportion of vacationers who plan to travel outside the United States in the next 12 months. Your estimate must be accurate within 3% of the true proportion.

(a) No preliminary estimate is available. Find the minimum sample size needed.

(b) Find the minimum sample size needed, using a prior study that found that 26% of the respondents said they planned to travel outside the United States in the next 12 months.

(c) compare the results from parts (a) and (b)

#### Solution Summary

The solution provides step by step method for the calculation of confidence interval and sample size for population proportion. Formula for the calculation and Interpretations of the results are also included. Interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.

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