SOLUTION: An instructor gives his class a set of 15 problems with the information that the next quiz will consist of a random selection of 4 of them. If a student has figured out how to do 7

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Question 367510: An instructor gives his class a set of 15 problems with the information that the next quiz will consist of a random selection of 4 of them. If a student has figured out how to do 7 of the problems, what is the probability the he or she will answer correctly at least 3 questions?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
# of ways 3 correct answers: C%287%2C3%29%2AC%288%2C1%29+=+280,
# of ways 4 correct answers: C%287%2C4%29%2AC%288%2C0%29+=+35.
# of ways getting 4 questions out of 15: C%2815%2C4%29=1365, thus the probability is %28280%2B35%29%2F1365+=+315%2F1365=+3%2F13