Availability of first truck probability P (1) = 0.74 Availability of second truck probability P (2) = 0.57 Availability of both truck probability P (1 and 2) = 0.46 So the probability of at least one available P (1 or 2) = P (1) + P (2) - P (1 and 2) = 0.74 + 0.57 - 0.46 = 0.85 Now the probability of at neither available = 1 - P (1 or 2) = 1 – 0.85 = 0.15