标题: 大全-2-14 [打印本页]
作者: excellences 时间: 2005-6-9 07:07 标题: 大全-2-14
A recent survey of all auto accident victims in doile 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 belts, drivers and front-seat passengers can greatly reduce their risk of being severly 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 fornt-seat passengers in dole County always wear seat belts when traveling by car.
(C) More drivers and front-seat passengers than rear-seat passagers were very serverly injured.
(D) More than half of the drivers and front-seat passangers 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 County do not involve any serioius injury.
为什么答案是A呢,怎么也想不明白，这到题应如何入手呢?这种问 percentage的题有何规律吗?
作者: sammen 时间: 2005-6-9 19:18
虽然我也没想明白,我给看看NN得解释
14题根据题意严重受伤的人中80％不使用安全带 结论是使用安全带降低严重受伤的风险 而如果全部受调查者中（包括严重受伤和受轻伤的人）也有80％或者以上人不使用安全带 那么使用安全带就对严重受伤没有影响甚至更加强可能性 原结论就不成立 反之 要使原结论成立 必须所有人中不使用安全带的比例小于80％那么使用安全带的人就要超过20％了
作者: sammen 时间: 2005-6-9 19:21
我想明白了.
超过20％的人带安全带，车祸中受伤的只有20％的人是带了安全带的，说明一部分带安全带的人没有受伤。说明安全带有用。如果说，带安全带的人不足20％，而受伤的人中带安全带的人有20％，那不是说明安全带没用了吗？
作者: conquer 时间: 2005-6-10 06:26
超过20％的人带安全带，车祸中受伤的只有20％的人是带了安全带的，说明一部
分带安全带的人没有受伤。说明安全带有用。如果说，带安全带的人不足20％，
而受伤的人中带安全带的人有20％，那不是说明安全带没用了吗？
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