分享一道PREP/OG逻辑难题 OG 13 CR #77 vehicles with radar detectors

Crystal_Chai

这是自己想了好久的题目，感觉有点难。查了Manhattan上Ron跟Stacey的解答，做个小小搬运工。另外再加一点自己的小体会。

A recent report determined that although only 3 percent of drivers on Maryland highways equipped their vehicles with radar detectors, 33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them. Clearly, drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are drivers who do not.

The conclusion drawn above depends on which of the following assumptions?

A   Drivers who equip their vehicles with radar detectors are less likely to be ticketed for exceeding the speed limit than are drivers who do not.  
B   Drivers who are ticketed for exceeding the speed limit are more likely to exceed the speed limit regularly than are drivers who are not ticketed.
C   The number of vehicles that were ticketed for exceeding the speed limit was greater than the number of vehicles that were equipped with radar detectors.  
D   Many of the vehicles that were ticketed for exceeding the speed limit were ticketed more than once in the time period covered by the report.  
E   Drivers on Maryland highways exceeded the speed limit more often than did drivers on other state highways not covered in the report.


正确答案： B


逻辑链：
Premise 1: 3% 的司机会给车子配备雷达探测器；
Premise 2: 因为超速罚款的车辆中有33%安装了雷达探测器。
Conclusion：那些给车子配备了雷达探测器的司机会经常超速。 （注意原题最后一句结论里面的"regularly"）

GAP： 吃罚单的司机就会经常超速了吗？如果只是因为有些司机偶尔点儿背被抓了呢？

所以如果要使原句的结论成立的话，必须要能够证明"装了雷达探测器的司机比没装的更会经常(regular)超速的习惯"----这也是选项B所想讲的。

注意FA类型的题目一定要根据原文题意去做判断，切忌加入自己的主观猜测。

其他的我就把Ron 跟Stacey的解释发过来。

Summary:
3% of all equipped with detectors
33% of vehicles caught speeding equipped with detectors
Conclusion: drivers who use detectors are more likely to speed regularly than those who don't

Author has made a leap between speeding only occasionally and getting (unluckily) caught vs. speeding regularly - but the rest of the argument does not actually mention anything about the frequency of speeding of various groups. It may be obvious that the more often you speed, the more chances you have to get caught - but the argument does not spell this out.

Choice B addresses this leap that the author makes about the frequency of speeding. If drivers who are ticketed are likely to exceed the speed limit regularly, then the 33% of vehicles caught speeding with detectors will fall into this category of people who are more likely to speed regularly. Remember, again, that it may be obvious that the more often you speed, the more likely you are to get caught - but the argument doesn't literally spell it out, and that's the point. The author is just assuming this point is true without spelling it out.

Choice A does not address author's conclusion - he's contending that drivers who choose to use detectors do so because they plan to speed regularly. This choice says that whether someone has a detector has a bearing on whether s/he gets caught - which may be true in the real world, but it does not answer this question.

D is incorrect because its content is irrelevant to the content of the passage.

the passage talks in terms of percentages of the number of VEHICLES ticketed - not percentages of the total number of tickets. therefore, even if certain vehicles were ticketed multiple times, nothing in the argument would change (because one vehicle still counts as one vehicle, even if it is pulled over multiple times).

also note that you're looking for an ASSUMPTION that is REQUIRED by the passage. if you pick an answer like d - which is clearly not REQUIRED by the argument, even if you don't immediately see why it's irrelevant - that probably means you aren't reading the question prompt correctly.

Crystal_Chai

自己给自己顶一个~

阿霖

我感觉我做的时候重点完全错了，我的点在于仅仅是3%和33%并不能说明装了雷达就更容易超速，毕竟分母不一样。不过后来想了想似乎这边的推断是对的，主要还是regular这边有gap。

ccp92

Mark一下！               

iso9

孜孜不倦， 吾等楷模 …………

ET游戏狂

隐藏部分是什么？

Crystal_Chai

iso9 发表于 2016-7-26 23:54
孜孜不倦， 吾等楷模 …………

Thanks~

-sarahsha

thanks!