(3) The manufacture of a certain part requires two different machine operations. The time on machine 1 has mean 4 hours and standard deviation 1 hour. The time on ma- chine 2 has mean 4.5 hours and...

Extracted text: (3) The manufacture of a certain part requires two different machine operations. The time on machine 1 has mean 4 hours and standard deviation 1 hour. The time on ma- chine 2 has mean 4.5 hours and standard deviation 1.5 hours. The times needed on the machines are independent. Approximate the probability that the total manufacturing time for 65 parts will be between 500 and 550 hours?