# confidence interval estimate

• Nov 30th 2009, 11:31 AM
desire150
confidence interval estimate
To compare the durabilities of two paints for highway use, 12 four-inch wide lines of each paint were laid down across a heavily-traveled road. The order was decided at random. After a period of time, reflectometer readings were obtained for each line. The higher the reading, the greater is the reflectivity and the better is the durability of the paint. The data are as follows:

Paint A: 12.5, 11.7, 9.9, 9.6, 10.3, 9.6, 9.4, 11.3, 8.7, 11.5, 10.6, 9.7

Paint B: 9.4, 11.6, 9.7, 10.4, 6.9, 7.3, 8.4, 7.2, 7.0, 8.2, 12.7, 9.2

What is the 95% confidence interval estimate for the difference between the mean reflectivity reading for Paint A and Paint B? Please complete the blank: “we can be 95% confident that the true difference between the actual means is
• Dec 1st 2009, 11:02 PM
matheagle
It looks like the population variances are equal so use....

$\displaystyle \bar X_1-\bar X_2\pm t_{22, .025}s_p\sqrt{ {1\over 12}+{1\over 12}}$