A simple random sample of 60 items resulted in a sample mean of 80. The population standard deviation is 15.
a. Compute the 95% confidence interval for the population mean. Round your answers to one decimal place.(___ ,____ )
b. Assume that the same sample mean was obtained from a sample of 120 items. Provide a 95% confidence interval for the population mean. Round your answers to two decimal places.(_____,_____ )
c. What is the effect of a larger sample size on the interval estimate?
Larger sample provides a _________margin of error.