A mass production line manufactures products of which 10% are faulty. A quality assurance (QA) expert samples products from the production line until he finds a defective product. a. What is the variable under study? (1.5) b. What is the probability that the QA expert sampled at least two products until he got the first defective product? (3) c. Find out the average number of sampled products to get the first defective product. (1.5) d. Also find out the standard deviation of the sampled products to get the first defective product. (1.5)