Confidence Interval
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1. The Internal Revenue Service is studying contributions to charity. The mean calculated from a random sample of 36 returns is $150. Assume that the population standard deviation is known and equal to $20. Construct a 98 percent confidence interval for the population mean.
2. A large bank believes that one-third of its checking customers have used at least one of the bank's other services during the past year. How large a sample is required to estimate the actual proportion within a range of plus and minus 0.04? Use the 98 percent level of confidence.
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