feifei logic 94

miffyhui

94. When 100 people who have not used cocaine are tested for cocaine use, on average only 5 will test positive. By contrast, of every 100 people who have used cocaine 99 will test positive. Thus, when a randomly chosen group of people is tested for cocaine use, the vast people is tested for cocaine use, the vast majority of those who test positive will be people who have used cocaine.
A reasoning error in the argument is that the argument
(A) attempts to infer a value judgement from purely factual premises
(B) attributes to every member of the population the properties of the average member of the population 没看懂选项
(C) fails to take into account what proportion of the population have used cocaine
(D) ignores the fact that some cocaine users do not test positive
(E) advocates testing people for cocaine use when there is no reason to suspect that they have used cocaine



B选项是个什么意思？ 就是在B、C选项中纠结

miffyhui

sdcar2010

Just think about this way.

What if "a randomly chosen group of people" happen to be "people who have not used cocaine ?"  Would the conclusion of the passage still holds?

No. Why? because the author assumes "a randomly chosen group of people" MUST reflect the average of the society, meaning it must have some people who use cocaine.

单调唱

Just think about this way.

What if "a randomly chosen group of people" happen to be "people who have not used cocaine ?"  Would the conclusion of the passage still holds?

No. Why? because the author assumes "a randomly chosen group of people" MUST reflect the average of the society, meaning it must have some people who use cocaine.

-- by 会员 sdcar2010 (2012/3/22 20:57:21)

说的好，一下子明白了！比狒狒逻辑上揭示的好！