Jack Welch, former CEO of General Electric, famously used a 20-70-10 "stack- ranking" system for his managers. The top 20% received bonuses and stock options, the middle 70% received no bonuses, and the bottom 10% was fired1. Assume that the performance of managers can be described by a normal distribution. Use Excel to calculate: a. How many standard deviations above the mean would a manager need to be to earn a bonus? b. How many standard deviations below the mean would a manager need to be to get fired?