Acontractor has two subcontractors for his excavation work. experience shows that in 60% of the time, subcontractor a was available to do the job, whereas subcontractor b was available 80% of the time. (a) what is the probability that both subcontractors will be available to do the job? (b) if the contractor learned that subcontractor a is not available for the job, what is the probability that the other subcontractor will be available? (c) suppose ea denotes the event that subcontractor a is available, and eb denotes that subcontractor b is available. (i) are ea and eb statistically independent? (ii) are ea and eb mutually exclusive? (iii) are ea and eb collectively exhaustive?