ah well I've got the solution and the concept. drawing venn diagrams certainly does help. i spent last night focusing on a purely graphical approach instead of a symbolic-computation approach on a different probability problem and solved it successfully. thank you for your guidance, Dick.
(I'll denote complements like this: c{A} for complement of A)
B is continuing to vex me. From the problem statement, I'm interpreting this: P(c{A}B U Ac{B}) = P(c{A}B) + P(Ac{B}) = 0.90; that is, if one is not available the contractor still has a 90% chance of being able to hire the other...
Homework Statement
A contractor has two subcontractors for his excavation work. Experience shows that in 60% of the time, subcontractor A was available to do a job, whereas subcontractor B was available 80% of the time. Also, the contractor is able to get at least one of these two...