question archive Manufacture of a certain component requires three different machining operations

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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 15, 30, and 20 minutes, respectively. The standard deviations are 1, 2, and 1.5 minutes, respectively. a) What is the expected values for the time to machine a randomly selected component? b) What are the variance and standard deviation for the time to machine a randomly selected component? c) What is the probability that it takes at most 1 hour of machining time to produce a randomly selected component? Provide the standard normal transformation and a summary statement. d) If the first step of the machining operation was always performed twice, what would be the expected value and variance for the time to machine a randomly selected

component?