- In past years, approximately 20% of all U.S. families purchased potato chips at least once a month. You are interested in determining the fraction of all U.S. families that currently purchase potato chips at least once a month. How many families must you survey if you want to be 99% sure that your estimate of the relevant proportion is accurate within 2%?
- Political polls typically sample randomly from the U.S. population to investigate the percentage of voters who favor some candidate or issue. The number of people polled is usually on the order of 1000. Suppose that one such poll asks voters how they feel about the President’s handling of environmental issues. The results show that 575 out of the 1280 people polled say they either approve or strongly approve of the President’s handling. Find a 95% confidence interval for the proportion of the entire voter population who approve or strongly approve of the President’s handling. If the same sample proportion were found in a sample twice as large—that is 1150 out of 2560—how would this affect the confidence interval? How would the confidence interval change if the confidence level were 90% INSTEAD OF 95%?
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