2014 AIME II Problem 2
Below is the professionally curated solution for Problem 2 of the 2014 AIME II, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2014 AIME II solutions, or check the answer key.
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Difficulty rating: 2110
2.
Arnold is studying the prevalence of three health risk factors, denoted by and within a population of men. For each of the three factors, the probability that a randomly selected man in the population has only this risk factor (and none of the others) is For any two of the three factors, the probability that a randomly selected man has exactly these two risk factors (but not the third) is The probability that a randomly selected man has all three risk factors, given that he has and is The probability that a man has none of the three risk factors given that he does not have risk factor is where and are relatively prime positive integers. Find
Solution:
Take a population of men and fill in a Venn diagram. Each of the three exactly-one regions contains men, and each of the three exactly-two regions contains If men have all three factors, then the men with both and number so the given conditional probability says giving
The union of the three sets therefore contains men, leaving with no risk factor. The men with risk factor number so men do not have
The desired probability is which is in lowest terms, so
Problem 2 in Other Years
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