"Durable Press" cotton fabrics are treated to improve their recovery from wrinkles after washing. Unfortunately, the treatment also reduces the strength of the fabric. A study compared the breaking strength of fabrics treated by two commercial durable press processes. Five swatches of the same fabric were assigned at random to each process. Here are the data, in pounds of pull needed to tear the fabric:
Permafresh 29.9 30.7 30.0 29.5 27.6
Hylite 28.8 23.9 27.0 22.1 24.2
A fabric manufacturer wants to know how large an advantage in strength fabrics treated by the Permafresh method have over the fabrics treated by the Hylite process. Give a 90% confidence interval for the difference in mean breaking strengths. (Use all 5 fabric swatches.)
The solution provides step by step method for the calculation of confidence interval for mean difference. Formula for the calculation and Interpretations of the results are also included.