• Find 80%, 85% and 99.9% confidence interval for the sample mean of a population, if we know that in a random sample of 70 people from the population, the sample mean is 60 and the standard deviation is 5.

A simple random sample of size n is drawn from a population that is known to be normally distributed. The sample mean, x¯\bar{x}xˉ, is determined to be 104.3 and the sample standard deviation, s, is determined to be 15.9. (a) Construct the 90% confidence interval for the population mean if the sample size, n, is 15. (b) Construct the 90% confidence interval for the population mean if the sample size, n, is 25. How does increasing the sample size affect the width of the interval? (c) Construct the 95% confidence interval for the population mean if the sample size, n, is 15. Compare the results to those obtained in part (a). How does increasing the level of confidence affect the confidence interval? (d) Construct the 90% confidence interval for the population standard deviation if the sample size, n, is 15.�

a simple random sample of 60 items resulted in a sample mean of 80. The population standard deviation is  15.

1. Compute the 95% confidence interval for the population mean.

2. Assume that the same sample mean was obtained from a sample of 120 items. Provide

   a 95% confidence interval for the population mean.

3. What is the effect of a larger sample size on the interval estimate?

How to construct a 95% confidence interval if the sample mean is 100, the population standard deviation is 17.5 and the size of the sample is 40?