5 A refrigerator has a lifetime with an average of 9 years I

5) A refrigerator has a lifetime with an average of 9 years. If the breakage events for refrigerators follow Poisson distribution, What is the probability that the refrigerator will last between 7 and 12 years?

6) 6 refrigerators as in question 5) are chosen independently. What is the probability that exactly 3 of them will last between 7 and 12 years?

Solution