A brand of bearings has a mean life span of 15,000 cycles, with a standard deviation of 1,250 cycles. Assume the life spans of the bearings have a bell-shaped distribution.

(a) The life spans of three randomly selected bearings are 13,500 cycles, 17,000 cycles, and 18,500 cycles. Find the z-score that corresponds to each life span. Determine whether any of these life spans are unusual.

(b) The life spans of three randomly selected bearings are 12,500 cycles, 14,750 cycles, and 19,000 cycles. Using the Empirical Rule, find the percentile that corresponds to each life span.