A company that owns and services a fleet of cars for its sales force has found that the service lifetime of disc brake pads varies from car to car according to a Normal distribution with mean µ = 55,000 miles and standard deviation σ = 4500 miles. The company installs a new brand of brake pads on 8 cars. The average life on the pads on these 8 cars turns out to be 51,800 miles. What is the probability that the sample mean lifetime is 51,800 miles or less if the lifetime distribution is unchanged?