大全-2-14

lindar1009

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?

berylgirls

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？

lindar1009

明白了，多谢

mingzhu

引用LIU9903 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？

这当中,超过20%的人带安全带基数是全体乘客,而后面车祸中受伤的只有20％的人是带了安全带的,基数是受伤的乘客,两者好象不是完全对等.迷惑.请接着讨论.

Avantasia

all auto accident victims 是一个比severly injured victims大的范围，如果范围缩小后比例反而增加，则说明条件对结果有促进作用

在所有受伤者中少于80％的人不带安全带（因为多于20％的人带了安全带），而在重伤者中有80％不带安全带，这说明不带安全带会导致严重受伤，即加强了结论