问一道逻辑假设题，实在想不明白,跪求详解

sunny20111126

A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that, by wearing seat belt, 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.(答案)
B) considerably more than 20 percent of drivers and front-seat passengers in Dole Country always wear seat belts when traveling by car.
C)More  drivers and front-seat passengers in the survey than rear-seat passengers were very severely injuried.
D) More than half of the  drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents.
E) Most of the auto accidents reported to police in Dole Country do not involve any serious injury.

sunny20111126

没有人会吗，还是问题太弱了啊？upup

sdcar2010

Necessary assumption. Use negation.

sunny20111126

但是不明白a为啥对？跟那个比例有啥关系嘛

sunny20111126

Necessary assumption. Use negation.

-- by 会员 sdcar2010 (2012/3/10 13:44:30)

再说得详细细点好不

luogengchi

问题是 哪个statement可以证明  ‘绑安全带可以减少车祸受伤’论据正确。
意在对比 绑安全带 和 不绑安全带 在出车祸受伤时的区别
那只要证明绑万全带的受伤率比不帮安全带的受伤率低就行了呗
原题说  80%出车祸受伤的人是因为没有绑安全带造成的
那第一个选项说多于20%的受伤的人在出车祸时绑安全带    意思就是说在所有出车祸受伤的人里面大多数人是没有绑安全带的 少数人是绑安全带的。 所以证明了 绑安全带可以减少车祸受伤。
逻辑为：没安全带---受伤，有安全带---不会受伤，a不会受伤就不会进入统计受伤的数据，b进入受伤数据统计的比例也要少于没有安全带的受伤的比例。

sdcar2010

You need to pay attention to details. "all auto accident victims" vs. "severely injured drivers and front-seat passengers."  The premise is that "80% of the severely injured drivers and front-seat passengers" were not wearing set belts.  The conclusion is 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."

What about those who were not injuried in an accident?  How many of them wearing seat belts?  If none of them wore seat belts, then the conclusion is wrong.

A is a necessary assumption.

sunny20111126

我是这样想的：原题说在所有受害者中
受重伤的：80%都没系安全带（是这意思吧，还是所有受害人中的80%？）那就是说剩下20%都
                系安全带了，也受重伤了。---＞所以他说系了安全带比不系安全带好。
轻伤的：没说（万一系了安全带的比不系安全带的人数目多呢）
挂了的：没说。（万一系了安全带的人全挂了呢？）
---＞那这样不就推出了系安全带很恐怖？
A说，在所有受害人中超过20%的人都系了安全带。（就是说剩下那不到80%的人都没系安全带？）
我不明白的是，A说得那more than 20%加上那80%不就超过100%了吗？所以这个20%和那个80%到底啥关系啊？
还请在帮我解释一下，着急死了，着急死了，着急死了

sunny20111126

问题是 哪个statement可以证明  ‘绑安全带可以减少车祸受伤’论据正确。
意在对比 绑安全带 和 不绑安全带 在出车祸受伤时的区别
那只要证明绑万全带的受伤率比不帮安全带的受伤率低就行了呗
原题说  80%出车祸受伤的人是因为没有绑安全带造成的
那第一个选项说多于20%的受伤的人在出车祸时绑安全带    意思就是说在所有出车祸受伤的人里面大多数人是没有绑安全带的 少数人是绑安全带的。 所以证明了 绑安全带可以减少车祸受伤。
逻辑为：没安全带---受伤，有安全带---不会受伤，a不会受伤就不会进入统计受伤的数据，b进入受伤数据统计的比例也要少于没有安全带的受伤的比例。

-- by 会员 luogengchi (2012/3/11 11:21:25)

受重伤的80%都没系安全带。那万一系了安全带的人全挂了呢？岂不是系安全带更危险了吗？
A在所有受害人中，超过20%的人系了安全带。就推出剩下那不到80%的人没系安全带。所以还是系安全带好，我明白了。

sunny20111126

You need to pay attention to details. "all auto accident victims" vs. "severely injured drivers and front-seat passengers."  The premise is that "80% of the severely injured drivers and front-seat passengers" were not wearing set belts.  The conclusion is 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."

What about those who were not injuried in an accident?  How many of them wearing seat belts?  If none of them wore seat belts, then the conclusion is wrong.

A is a necessary assumption.

-- by 会员 sdcar2010 (2012/3/11 13:01:07)

我是这样想的：原题说在所有受害者中
受重伤的：80%都没系安全带（是这意思吧，还是所有受害人中的80%？）那就是说剩下20%都
               系安全带了，也受重伤了。---＞所以他说系了安全带比不系安全带好。
轻伤的：没说（万一系了安全带的比不系安全带的人数目多呢）
挂了的：没说。（万一系了安全带的人全挂了呢？）
---＞那这样不就推出了系安全带很恐怖？
A说，在所有受害人中超过20%的人都系了安全带。（就是说剩下那不到80%的人都没系安全带？）
我不明白的是，A说得那more than 20%加上那80%不就超过100%了吗？所以这个20%和那个80%到底啥关系啊？求求您再帮我解释一下，我这时错哪了？着急死了，着急死了，着急死了