The lengths of text messages are normally distributed with a population standard deviation of 6 characters and an unknown population mean. If a random sample of 21 text messages is taken and results in a sample mean of 24 characters, find a 99% confidence interval for the population mean. Round your answers to two decimal places.
z0.10 | z0.05 | z0.04 | z0.025 | z0.01 | z0.005
1.282 | 1.645 | 1.751 | 1.960 | 2.326 | 2.576
You may use a calculator or the common z-values above.
Select the correct answer below:
(21.85, 26.15)
(21.43, 26.57)
(21.71, 26.29)
(20.95, 27.05)
(22.32, 25.68)
(20.63, 27.37)