The absentee rate for bus drivers in a large school district has been 5% in recent years. During the past few months, the school district and the bus drivers' union have been engaged in negotiations for a new contract. Negotiations are at an impasse over several key issues, and the drivers already have worked 6 months past the termination of their previous labor contract with the district. Yesterday's negotiating session was particularly contentious, with members of both sides engaging in heated debate and name-calling.
Of the 400 bus drivers who serve the school district, 60 of them called in sick this morning, an absentee rate of 15%. The school district has accused the union of collusion in carrying out a work stoppage and the union has responded that the school district is just trying to make a big deal out of more people than usual happening to be sick on a given day.
Given the historical absentee rate, what is the probability that a daily absentee rate would happen to be 15% or more? Comment on the competing claims of the school district and the bus drivers' union.