A professor's sample estimated the standard deviation of missing assignments to be 3 . You are researching the average missing assignments. You want to know how many people you should survey if you want to know, at a 90 % confidence level, that the sample mean amount of missing assignments is within 1 assignments of the true mean number of missing assignments. Use a calculator to find the z - value that you should you use to calculate the 90 % confidence level. Round your answer to three decimal places