Bunuel wrote:

A certain businessman wears only three different colors of shirt - white, blue and grey. The probability that he will wear a blue or grey shirt is 2/3. During a four-day work week, what is the probability that the businessman will wear a white shirt at least once?

(A) 16/81

(B) 2/3

(C) 8/27

(D) 65/81

(E) 19/27

We can use the following equation:

1 = P(wearing white shirt at least once) + P(not wearing white shirt at all)

P(wearing white shirt at least once) = 1 - P(not wearing white shirt at all)

Since P(not wearing white shirt at all) = P(wearing blue or grey shirt all 4 days), that gives us (2/3)^4 = 16/81, and thus:

P(wearing white shirt at least once) = 1 - 16/81 = 65/81

Answer: D

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Scott Woodbury-Stewart

Founder and CEO

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