Why is it important to know the population standard deviation when estimating the population mean? Multiple choice question. Knowing lets us use the standard normal distribution to construct a confidence interval. The mean is used in calculating the population standard deviation. The sample standard deviation cannot be used to estimate the population standard deviation.A sample of size 25 is taken from a population with standard deviation 6. The sample mean is 10. Which of the following is a 99% confidence interval for the population mean? Multiple choice question. 6.9 to 13.1 7.42 to 12.58 8.8 to 11.2 -5.48 to 25.48