请教一道逻辑题

britney_gao · 发表于 2003-3-31 11:15:00

A recent survey of all auto accident victims in Dole Couty found that,of the severely injuried drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that , by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.
The conclusion above is not properly drawn unless which of the following is true?
(A) Of all the drivers and front-seat passengers in the survey ,more than 20 percent were wearing seat belts at the time of their accidents.
(B) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when travelling by car.
(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.
(D) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accident.
(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.
正确答案选A。但是我不明白两个比例之间到底有什么关系

chipmunk · 发表于 2003-3-31 11:39:00

Britney, 你可以从反面来理解答案A。假设只有10%的人寄安全带，那么就有90%的人没有寄；同时在严重受伤的人里面，有20%寄了安全带，80%的人没有寄。根据这些可以推出如果<20%寄安全带的话，那么寄安全带的人里面受伤的比例还比不寄的要高。

这样从反面证明了A是一个必要条件。

Bensontuo · 发表于 2019-8-20 16:59:06

britney_gao 发表于 2003-3-31 11:15
A recent survey of all auto accident victims in Dole Couty found that,of the severely injuried drive ...

Spot the question type: Necessary Assumption

80% of severely injured drivers no wear the seat belts, 20 % of severely injured drivers did wear the seat belt.

However, what about the drivers not severely injured ? Did they wear the seat belts or not ?

結論要看清楚, 首先, 我們只有比較了嚴重受傷的人戴以及不戴安全帶的比例, 可是那些不嚴重受傷人有沒有帶以及整體受傷的駕駛的統計數字我們是不知道的。

而如果本文的結論在於, 如果嚴重受傷的人數可以大幅度的減少, 必定是因為戴安全帶的關係。那那些沒有嚴重受傷的人有沒有帶安全帶的比例就相當重要了

等於, 總體沒帶安全帶的人的且受傷的人數一定要大於總體有戴安全帶但是沒有受傷或是輕傷的人數。

A. " No more than " 20% were wearing seat belts at the time of their accidents

如果少於20% 的人戴安全帶, 那就代表, 沒帶安全帶的人數裡面還是有一部分是輕傷的, 那如果沒戴安全帶的人數裡面有一部分是輕傷的, 你就不能夠說帶了安全帶可以減少重傷的比例。

请教一道逻辑题

请教一道逻辑题

所属分类: GMAT考试

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