The breaking strengths of n =20 bundles of wool bers have

Chapter 9, Problem 9.3.7

(choose chapter or problem)

The breaking strengths of n =20 bundles of wool bers have a sample mean x =436.5 and a sample standard deviation sx =11.90. In addition, the breaking strengths of m =25 bundles of synthetic bers have a sample mean y =452.8 and a sample standard deviation sy =4.61. Answer the following questions without assuming that the two population variances are equal. (a) Does a one-sided hypothesis test with size =0.01 accept or reject the null hypothesis that the synthetic ber bundles have an average breaking strength no larger than the wool ber bundles? (b) What is a one-sided 99% condence interval that provides an upper bound on A B, where A is the average breaking strength of wool ber bundles and B is the average breaking strength of synthetic ber bundles? (c) Is there enough evidence to conclude that the average breaking strength of synthetic ber bundles is larger than the average breaking strength of wool ber bundles? (This problem is continued in 9.7.12.)