17.31 How strong are durable press fabrics? "Durable press" cotton fabrics are treated to improve their recovery from wrinkles after washing. Unfortunately, the treatment also re duces the strength of the fabric. A study compared the breaking strength of fabrics treated by two commercial durable press pro cesses. Five swatches of the same fabric were assigned at random to each process. Here are the data, in pounds of pull needed to teat the fabric:'^

Permafresh j 29.9 30.7 30.0 29.5 27.6 Hylite ! 28.8 23.9 27.0 22.1 24.2 Is there good evidence that the two processes result in different mean breaking strengths?

(a) Do the sample means suggest that one of the proces,ses is superior in breaking strength?

(b) Make stemplots for both samples. The Permafresh sample contains a mild outlier. With just 5 observations per group, we worry that this outlier will affect our conclusions.

(c) Test the hypothesis Hq: iJi\ = jxi against the two-sided al ternative twice: once using all the data and again without the outlier in the Permafresh sample. Do the two tests lead to similar conclusions? Can we safely conclude that one treat ment has significantly higher mean breaking strength than the other?