For a 95 confidence level the necessary value for z x za 2 0 x za 2 Step 4 We now have all the values necessary to find the upper and lower bounds for the confidence interval x 33 Za 2 1 960 o 7 and n 50 Substitute these values to first find the lower bound of the 95 confidence interval to two decimal places D 50 n 99 6 n 33 2 576 Now find the upper bound of the 95 confidence interval to two decimal places 50 33 is 1 960 Za 2 1 960 Submit Skip you cannot come back Thus a 95 confidence interval for the population mean in a sample of 50 items with a sample mean of 33 and a population standard deviation of 7 is to