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Confidence Interval and Sample size

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1. Suppose you want an 85 percent confidence level. What value would you use to multiply the standard error of the mean?

2. Dr. Patton is a professor of English. Recently he counted the number of misspelled words in a group of student essays. For his class of 40 students, the mean number of misspelled words was 6.05 and the standard deviation 2.44 essay. Construct a 95 percent confidence interval for the mean of misspelled words in the population of student essays.

3.We want to estimate the population mean within 5, with a 99 % level of confidence. The population standard deviation is estimated to be 15. How large a sample is required?

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Calculation of Confidence Interval and Sample size.

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