# Confidence Interval and Sample size

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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#### Solution Summary

Calculation of Confidence Interval and Sample size.

$2.19