Problem 9: Quality Assurance Department of company Vsmart, has stated that 9% of their phones are defective. a. If a customer randomly buy 10 of their phones, what is the probability that customer can find at least 8 working phone? b. Assume that they ship phones in lots. If there are 10 lots in a shipment, what is the probability at least 2 lots will have at most 7 working phones among 10 randomly selected phones. c. The Quality Assurance Department now correct their own statement after a crisis in operation system of their phones. Beside the 9% completely defective, now they also have 31% of their phones are software broken but still repairable. Given those conditions, what is the probability that exactly 4 phones are working among 10 randomly selected phones?