A company that produces fine crystal knows from experience that 10% of its goblets have cosmetic flaws and must be classified as "seconds".
a. Among six randomly selected goblets, how likely is it that only one is a second?
b. Among six randomly selected goblets, what is the probability that at least two are second?
c. It goblets are examined one-by-one, what is the probability that at most five must be selected to fine four that are not second?