A manufacturer of parts for automobiles knows that the proportion of defec¬

tive parts in the past has been about 10 percent. However, today he has taken a random sample of 10 parts and found that 2 were defective. What is the probability of his getting two or more defective parts by chance in such a sample if the probability of a defective part is only .10? Would you say that his finding suggests strongly that more defective parts than usual are being turned out?

10.A pair of dice are rolled for a total of four trials. If the dice are fair, find the probability that the dice total to 7 on exactly 3 of the four trials. Find the probability that the dice total to 7 on at most 2 of the 4 trials. What is the expected number of trials (out of four) that the dice will total to 7?