In 1999, nearly 500,000 Americans underwent laser surgcry to correct their vision. While the majority of patients were pleased with the results, it is estimated that 1% of patients of corneal specialists and 5% of patients of less experienced ophthalmologists have serious post-laser vision problems (Time, Oct. 11,1999).

a. If all 500,000 patients were operated on by corneal specialists, what is the expected number of patients who will experience serious post-laser vision problems? Answer the same question assuming all patients are operated on by ophthalmologists.

b. If 400 employees of a particular company choose to undergo laser surgery with ophthalmologists, what is the approximate probability that 20 or more of these employees will suffer serious vision problems? Justify the methodology you used to answer the question.

c. Refer to part

b. Can the same methodology be used to answer the same question assuming all 400 employees had chosen a corneal specialist'? Explain.