Step 1 :Define the null hypothesis as the mean mpg of the car being 31, and the alternative hypothesis as the mean mpg being less than 31.
Step 2 :Given the sample mean (29.4), the sample standard deviation (9), and the sample size (54), calculate the t statistic and the p-value.
Step 3 :Calculate the t statistic using the formula \(t = \frac{{\bar{x} - \mu}}{{s/\sqrt{n}}}\), where \(\bar{x}\) is the sample mean, \(\mu\) is the population mean, s is the sample standard deviation, and n is the sample size. The calculated t statistic is approximately -1.306.
Step 4 :Calculate the p-value using a t-distribution table or a statistical software. The calculated p-value is approximately 0.099.
Step 5 :Compare the p-value with the significance level (0.01). Since the p-value is greater than the significance level, fail to reject the null hypothesis.
Step 6 :Conclude that there is not enough evidence to support the claim that the mean mpg of the car is less than 31.
Step 7 :Final Answer: \(\boxed{\text{Fail to reject the null hypothesis}}\)