Question

An employee's email sample estimated the standard deviation of punctuation errors to be 4 errors. You are researching the average number of punctuation errors. You want to know how many people's emails you should survey if you want to know, at a 90% confidence level, that the sample mean number of punctuations errors is within 1 error of the true mean number of punctuation erros.

Use Excel to calculate the z-value that you should use for a 90% confidence level. Round your answer to three decimal places.

Answer 1

Given,

For two tailed test,

In excel,

We know that,

On squaring both side, we have,