8.21 Is there a difference in the yields of different types of investments? The file Index Return contains data about the performance of 38 indexes across the world as of July 2018. Source: Data extracted from bit.ly/2yS1QcS. a. Construct a 95% confidence interval estimate for the mean yield of one-year returns. b. Construct a 95% confidence interval estimate for the mean yield of five-year returns. c. Compare the results of (a) and (b)