Question

For a sample of nine automobiles, the mileage (in 1000s of miles) at which the original front brake pads were worn to 10% of their original thickness was measured, as was the mileage at which the original rear brake pads were wom to 10% of their original thickness. The results are given in the following table Front 32.8 26.6 35.6 36.4 29.2 40.9 40.9 34.8 36.6 Rear 39.8 35.2 46.1 46 39.9 51.7 51.6 46.1 47.3 Automobile 2 4 7 Let Hx represent the population mean for rear brake pads and let y represent the population mean for front brake pads. Find a 95% confidence interval for the difference ?D=??_??. Round the answers to three decimal places The 95% confidence interval for the difference in mean is 11.047 , -8.930 ).

Answer 1

Confidence interval formula for paired t test.

Sp D tt*

Where, t critical value = 2.306...................by using t table or by using Excel command =TINV(0.05,8)

Therefore,

1.38 9.992.306* V9

$=>9.99\pm 1.061$

=>(8.929,11.051)