In a survey of 150 senior executives, 47% said that the most common job interview mistake is to have little or no knowledge of the company.

a. If 6 of those surveyed executives are randomly selected without replacement for a follow-up survey, find the probability that 3 of them said that the most common job interview mistake is to have little or no knowledge of the company.

b. If part (a) is changed so that 9 of the surveyed executives are to be randomly selected without replacement, explain why the binomial probability formula cannot be used.