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**jpmckell** A manufacturer of a certain component requires 3 different machining operations. Machining time for each operation has a normal distribution and the three times are independent of one another. The mean values are 15, 30, and 20 minutes respectively and the standard deviations are 1, 2, and 1.5 minutes respectively. What is the probability that it takes at most 1 hour of machining time to produce a randomly selected component?

I do not know where to start on this problem, and would greatly appreciate help in solving it. Thank-You.