The following samples are observations taken from the same elements at two different times:

Unit Sample 1 Sample 2 1 15.1 4.8 2 12.3 5.7 3 14.9 6.2 4 17.5 9.4 5 18.1 2.3 6 18.4 4.7

a. Assume that the populations are normally distributed and construct a 90% confidence interval for the difference in the means of the distribution at the times in which the samples were taken.

b. Perform a test of hypothesis to determine if the difference in the means of the distribution at the first time period is 10 units larger than at the second time period. Use a level of significance equal to 0.10.