6. A manufacturing plant receives a shipment of 31 precision parts, including 4 that are defective. The plant will return the entire shipment if quality control finds 1 or more parts to be defective. If quality control picks six parts at random, what is the probability that the shipment is returned? 7. In one of her math education courses, Megan receives six different grades of 74, 88, 83, 78, 95, and 69. Find the (a) mean, and (b) standard deviation of her grades in the class. (Show how each is found, don't just write the answer from a calculator.)