Suppose lengths of text messages are normally distributie and have a known population standard deviation of 3 characters and an unknown population mean Arandon Sample of 20 text messays is taken and Sample mean of 31 characters gives a Identify the parameters needed to calculate a confidence interval at the 90 confidence level Then find the confidence interval 20 10 1 982 1 645 use the common z values given above Round the final answer to two decimal places if necessary IX 100 x 6 Z 0 05 Z 0 005 2 0 01 20 005 1 960 2 324 2 574 z g