Need help with statistics problem for finding time and cost for manufacturing

geromephoto

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Nov 2, 2015
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Manufacture of a certain component component requires three different machining operations. The amount of time each operation requires (operation time) is normally distributed with mean of 10 (in minutes) and variance 4. The Three operations are independent. Im thinking this means x ~ N(10, 4)

1) For a randomly selecte component, what is the probability that the average of the three operation times is less than 9 mins?

2) The cost for the first machining is 1$ per min, the second is 2$ and third is 3$ per min. What is the probability that the total cost for manufacturing the next component is more than 70$?
 
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