SOLUTION: a student takes an exam containing 12 true or false questions if the student guesses what is the probability that he will get exactly 2 questions right?

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Question 1031741: a student takes an exam containing 12 true or false questions if the student guesses what is the probability that he will get exactly 2 questions right?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Choose any two out of the 12 questions, which can be done in C(12,2) = 66 ways. (The only choice for each one of these is the correct answer.) After doing this, for each of the remaining 10 incorrectly-answered questions, there are two choices, either the wrong answer or a no answer at all, which can be done in 2%5E10+=+1024 ways.
Therefore the probability is %28C%2812%2C2%29%2A2%5E10%29%2F3%5E12+=+%2866%2A1024%29%2F531441+=0.127, to three significant figures.