Jinbao produces tubas and ships them in lots of twenty. Suppose that 60% of all such lots contain no defective tubas, 30% contain one defective, and 10% contain two defectives. Now suppose that a lot is inspected, with two tubas being selected from it at random, and neither is found to be defective.
a. What is the probability that there are no defectives in that lot?
b. What is the probability that there is one defective in that lot?