In an article entitled "Fuel Economy Calculations to Be Altered," James R. Healey indicated that the government planned to change how it calculates fuel economy for new cars and trucks. This is the first modification since 1985. It is expected to lower average mileage for city driving in conventional cars from 10% to 20%. AAA has forecast that the 2008 Ford F-150 would achieve 15.7 mile per gallon (mpg). The 2008 Ford F-150 was tested by AAA members driving the vehicle themselves and was found to have an average of 14.3 mpg. Assume that the mean obtained by AAA members is the true mean for the population of 2008 Ford F-150 trucks and that the population standard deviation is 5 mpg. Suppose 100 AAA members were to test the 2008 F-150. Determine the probability that the average mpg would be at least 15.7.
A) 0.0026
B) 0.0121
C) 0.0451
D) 0.0001

Question

Quizplus · Accepted Answer

The probability can be calculated using the standard normal distribution. The standard error is 5/sqrt(100) = 0.5. The z-score for 15.7 is (15.7 - 14.3) / 0.5 = 2.8. The probability of a z-score being at least 2.8 is approximately 0.0026.

In an Article Entitled "Fuel Economy Calculations to Be Altered