Refer to Exercise 10.30. Now assume that the shredding times for both paper shredders are normally distributed with unequal and unknown standard deviations.
a. Construct a 99% confidence interval for the difference between the two population means.
b. Using a 1% significance level, can you conclude that the mean time taken by the Piranha to shred 100 sheets is higher than that for the Crocodile?
c. Suppose that the sample standard deviations were 7.40 and 4.60 seconds, respectively. Redo parts a and b. Discuss any changes in the results.
d. What would your decision be in part b if the probability of making a Type I error were zero?