18. Sports Car: Fuel Injection The manufacturer of a sports car claims that the fuel injection system lasts 48 months before it needs to be replaced. A consumer group tests this claim by surveying a random sample of 10 owners who had the fuel injection system replaced. The ages of the cars at the time of replacement were (in months):

29 42 49 48 53 46 30 51 42 52 i. Use your calculator to verify that the mean age of a car when the fuel injection system fails is x 5 44.2 months, with standard deviation s < 8.61 months.

ii. Test the claim that the fuel injection system lasts less than an average of 48 months before needing replacement. Use a 5% level of significance.