A manufacturer claims that the life span of its tires is 48,000 miles. You work for a consumer protection agency and you are testing these tires. Assume the life span of these tires is normally distributed. You select 100 tires at random and test them. The mean life span is 47,785 miles. Standard deviation = 900 Assume the manufacturers claim is correct, what is the probability the mean is 47,785 or less?