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
133	189
131	159
118	181
110	184
148

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.
  
• The mean and the standard deviation for the Hylite are:
  
  ¯x=

Round to 3 decimal places.

s=

The standard error is:

SE = Round to 3 decimal places.

The critical value from the distribution for a confidence interval of 99.8% is:

t*= Use degrees of freedom of 3. Use Technology Round to 3 decimal places.

Using the the answer from above (all rounded to 3 decimal places), calculate by hand a 99.8% confidence interval for the difference in mean wrinkle recovery angle:

to . Hint Round to 3 decimal places.

Answer 1

a)

	Permafresh	Hylite
	133	189
	131	159
	118	181
	110	184
	148
xbar	128	178.25
sd	14.646	13.251

standard error = 9.43484

df =n1+n2-2 = 7

t = 4.785

confidence interval is

(-95.396 , -5.104)