Are the mpg measurements similar? 

Refer to Exercise 6.26 (page 371). In addition to the computer computing mpg, the driver also recorded the mpg by dividing the miles driven by the number of gallons at each ?ll-up. The following data are the differences between the computer's and the driver's calculations for that random sample of 20 records. The driver wants to determine if these calculations are different. Assume the standard deviation of a difference to be σ = 3.0.

5.0    6.5    -0.6    1.7    3.7    4.5    8.0     2.2      4.9        3.0

4.4    0.1       3.0    1.1    1.1    5.0    2.1    3.7    -0.6     -4.2

(a) State the appropriate H0 and Ha to test this suspicion.

(b) Carry out the test. Give the P-value, and then interpret the result in plain language.