A simple random sample of 10 items resulted in a sample mean of 20. The population standard deviation is = 10. 

a. Compute the 95% confidence interval for the population mean. Round your answers to one decimal place. Enter your answer using parentheses and a comma, in the form (n1,n2). Do not use commas in your numerical answer (i.e. use 1200 instead of 1,200, etc.) 

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.