A study found that for 60% of the couples who have been married 10 years or less, both spouses work. A sample of 30 couples who have been married 10 years or less are selected from marital records available at a local courthouse. We are interested in the number of couples in this sample in which both spouses work. What is the probability that this number is:
(a) 20 or more?
(b) 25 or more?
(c) 10 or fewer?
(Use the normal approximation.)