All seasons plumbing has two service trucks that frequently need repair. if the probability the first truck is available is .74, the probability the second truck is available is .57, and the probability that both trucks are available is .46:

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

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