Compute probabilities for means using the normal probability distribution. The average weekly earnings of bus drivers in a city are $950 (that is µ) with a standard deviation of $45 (that is σ). Assume that we select a random sample of 81 bus drivers. a. Assume the number of bus drivers in the city is large compared to the sample size. Compute the standard error of the mean. b. What is the probability that the sample mean will be greater than $960?