A quality control engineer inspects a random sample of two hand-held calculators from each incoming lot of size 18 and accepts the lot if they are both in good working condition; otherwise, the entire lot is inspected with the cost charged to the vendor. What are the probabilities that such a lot will be accepted without further inspection if it contains
(a) 4 calculators that are not in good working condition;
(b) 8 calculators that are not in good working condition;
(c) 12 calculators that are not in good working condition?