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Suppose that the introduction of a preventive maintenance program is deemed cost effective. Which of the following is most likely true if the cost to actually perform preventive maintenance is very expensive? Repairs carry little non-monetary consequences. low Cost to Repair The system never fails. low standard deviation in MTBF high standard deviation in MTBF The main difference between PERT and CPM is that PERT assumes that activity durations are known. PERT ignores activity costs. they differ in terminology and in the construction of the network. CPM assumes that activity durations can vary. PERT is more accurate than CPM. Which of the following statements regarding PERT analysis is true? Project standard deviation is the sum of all critical activity standard deviations. Each activity has two estimates of its duration. Only non-critical activities contribute to the project variance. Only critical activities contribute to the project variance. Project variance is the sum of all activity variances