According to “Trucker” magazine, the average life of a set of “Eternity” spark plugs is normally distributed, with a mean of 20,000 miles and a standard deviation of 1,000 miles. Bud Adams, the owner of a fleet of trucks, believes the Eternities actually last longer and decides to conduct an experiment. Bud installs Eternities in 40 of his trucks. At the end of the experiment, Bud collects his sample data and finds that the average life of his sample of Eternities is 20,550 miles.

Given: Level of significance = 10%. H0: µ  ≤  20,000     H1: µ > 20,000    

Question: What is your decision about the Null, supported by the computed test statistic and the critical value of Z?