Question

"Durable press" cotton fabrics are treated to improve their recovery from wrinkles after washing. "Wrinkle recovery angle" measures how well a fabric recovers from wrinkles. Higher is better. Here are data on the wrinkle recovery angle (in degrees) for the same fabric specimens discussed in the previous exercise:

Permafresh	Hylite
147	187
155	140
126	183
122	162
116

A manufacturer wants to know how large is the difference in mean wrinkle recovery angle.

1. The mean and the standard deviation for the Permafresh are:
   
   ¯x= _________ Round to 3 decimal places.
   
   s=_________ Round to 3 decimal places.
   
2. The mean and the standard deviation for the Hylite are:
   
   ¯x=__________ Round to 3 decimal places.
   
   s=___________ Round to 3 decimal places.
   
3. The standard error is:
   
   SE =___________ Round to 3 decimal places.
   
   The critical value from the distribution for a confidence interval of 95% is:
   
   t*= _____________Use degrees of freedom of 3. Use Technology Round to 3 decimal places.
   
4. Using the the answer from above (all rounded to 3 decimal places), calculate by hand a 95% confidence interval for the difference in mean wrinkle recovery angle:
   
   _________to________ . Hint Round to 3 decimal places.

Answer 1

Let denote mean wrinkle recovery angle for Permafresh and Hylite respectively.