Manufacture of a certain component requires three 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 20, 15, and 30 min, respectively, and the standard deviations are 2, 1, and 1.8 min, respectively. What is the probability that it takes at most 1 hour of machining time to produce a randomly selected component