A 95 % confidence interval for is ( x z / 2 n , x + z / 2 n ) . Here, = 0.05 and n = 49 . Since 2 = 1,369 that means = 37 . Use Excel to calculate the 95 % confidence interval. 1. Open Excel, enter the given data in column A, and find the sample mean, x , using the AVERAGE function. Thus, the sample mean, rounded to two decimal places, is x = 251.78 . 2. Click on any empty cell, enter = CONFIDENCE.NORM ( 0.05 , 37 , 49 ) , and press ENTER. 3. The margin of error, rounded to two decimal places, is z / 2 n 10.36 . The confidence interval for the population mean has a lower limit of 251.78 10.36 = 241.42 and an upper limit of 251.78 + 10.36 = 262.14 . Thus, the 95 % confidence interval for is ( 241.42 , 262.14 ) . copy this form next time for a similar