ChaseDream

标题: 关于og12 cr78超速吃罚单的题，小弟再次遇到又研究了一下，试着解释解释，求各牛拍砖 [打印本页]

作者: pirate舟 时间: 2012-3-25 04:05
标题: 关于og12 cr78超速吃罚单的题，小弟再次遇到又研究了一下，试着解释解释，求各牛拍砖
Q78.

A recent report determined that although only 3 percent of drivers on Maryland highways equipment 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 detecters are more likely to exceed the speed limit regularly than are drivers who do not.

the conclusion drawn above depends on which of the assumotions?

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 likely to exceed the speed limit reguarly 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 vehicels that were ticketed for exceeding the speed limit wre located more than once in the time period covered by the report.
E Drivers on Maryland highways exceeded the speed limit more often than diDd drivers on other state highways not covered in the report

题目结论是：装r 的比没有装r 的 regulary 更可能超速。

首先解决一个前提：就是假设没有gap，3%和33%两个比例也是不可以直接拿来比较从而得出结论的，因为这两个比列的涉及的主体都不同（一个是总车数，一个是被ticket的车数），是不可以用直觉来感觉一下的。那么是怎么比较的呢？
就是用（‘装r的超速车’ 占 ‘装r的总车数’的比例）与（‘没装r的超速车’ 占 ‘没装r的总车数’的比例）来比较，就是用
(33%*超速车)/ (3%*总车) 与 (66%*超速车)/ (97%*总车) 来比较
显然，前者大于后者，所以就会得到 “装r 的比没有装r 的更可能超速” 的结论。

那么接下来就会发现题目的结论和上面的比较是有gap的，而这个gap 就是regularly！就是说上面的比较是基于一次调查得到的数据（题目一开始说”A recent report determined that.." ），那么要得到结论中的regularly，就要考虑调查以外的情况，来排除这次调查的个别性。

在看题目之前，根据上面的分析，我们先来解释一个题目中将会出现新概念，就是 “被ticket的车”，它在这里所指的就是针对这次调查来说的，也就是 “被ticket的车”是指在调查中的超速车，而之前我们一直讨论的超速车，就是在regularly 情况下所说的超速车。

这样一分析以后，og对选项的解释就是就非常明了了，我们来看题目和解释：
A 装r车的比没r的车更不可能被ticket------------用og的解释 “这个说法很可能是对的，但是它与要推论道regularly的结论无关（not relevant）"
B 被ticket的车比没被ticket的车regularly更可能超速-------------发现没有，这里就正好确保了当跳出调查以后，在regularly时这个调查依然具有可信度。而这个调查在regularly时是否有可信度就是这题的assumption。
C
D 在调查中，大部分被ticket的车都是被ticket了多于1次的----------------依然用og，“这个也许可以支持结论，但是并不necessary，因为它只是针对单次的调查来说事，并不是一个general的情况。”
E

作者: sdcar2010 时间: 2012-3-25 04:20
You analysis missed the difference between being ticketed and exceeding speed limit. And your analysis, especially the equation you presented, hinges on the ASUMPTION that the speeding ticket reflects the speeding action. And this assumption is B). Therefore, your analysis is a circular reasoning.

作者: pirate舟 时间: 2012-3-25 05:01

You analysis missed the difference between being ticketed and exceeding speed limit. And your analysis, especially the equation you presented, hinges on the ASUMPTION that the speeding ticket reflects the speeding action. And this assumption is B). Therefore, your analysis is a circular reasoning.

-- by 会员 sdcar2010 (2012/3/25 4:20:08)

对的，我也发现了这一点我没有在分析里面说清楚了，但是我的观点是：在调查中，被ticket车的就是超速车！而被ticket车和超速车的区别是，“被ticket车”是在调查中对超速车的称呼，而“超速车”则是指regularly情况下的。也就是说，调查中并不存在“没有被ticket的超速车”。

我有两个理由：1如果在调查中还存在没有被ticket的超速车，那么那个评判谁更可能超速的公式将引入一个新的变量，那么整个题目就会变有异常多的要去推论的地方，如果你仔细写出来去分析的话就会发现这是不可能在gmat中做到的，或只用B中的那个一个assumption是说明不了更可能的，因为就像我说的不能凭感觉去用题目中两个关系很远的比例来比较出谁更已超速
2在一个一段时间的调查中，不遗漏地讲每一辆超速车都ticket也是可能的，而且根据og对各选项的解释，我们会发现，他关注的只是regularly的问题，也就像我分析那样，用公式得出一个针对调查的结论，而需要的是一个普遍的结论。而这里面被ticket是针对调查中来说，超度是针对普遍来说。

那么为什么会有被ticket和超速两种说法呢，我觉得也是可以理解的。在一个调查中，我们为了强调数量，说这段时间有多少多少辆车吃了罚单，而在说一个普遍的结论的时候，我们说某某车更容易超速。

感谢sdcar大牛的关注啊，还请再看一眼题目与我的分析，并对比og的解释。也还请继续对我提出批判啊！

作者: pirate舟 时间: 2012-3-25 12:07
-- 最后一行不知道为什么变小了。感谢sdcar2010大牛的关注，还请再想一想我提出的看法，因为和之前大家讨论的有些出入，并且我觉得按我这样理解更符合og对这题的解释，而且个人也觉得没有大的漏洞。
也希望其他高手前来拍砖。。。把这道题说清楚

我的看法主要有两点不同
1、就是我在楼上提出的被ticket的车和超速车数量上相同。
2、是评判谁更容易超速上。我认为直接用3% 和 30%的差别来感觉是没有道理的，比较谁更容易超速，要用“自己范围内的超速车”占“这个范围里的总车数”的比例来比较，就是最初的公式。
如果被ticket车和超速车不同，那么要比较可能性的公式就变成
（x*超速车)/（3%*总车) 与【（1-x)*超速车】/（97%*总车) 比较-------------x是超速车中安装了radar的比例

当超速车=被ticket车时，x=33%. 如果他们不等，x就是未知的。就算加入了B选项的assumption也不是充分的可以得出谁更可能超速的结论（这里都还没涉及regularly的情况），虽然有了B以后前者是可能大于后者的，但是没有B 也有可能（具体可以带入一个数值看一下）。

我的这个看法，只是在评判谁更可能超车上有点绕，但是一旦确定了，其实“被ticket车”和“超速车”一致时，那么这道题就变成：一个特殊的结论，需要一个assumption，然后的出一个普遍的结论。

那么在解题的时候，就一点也不绕了。而且很符合og对每个选项的解释。

作者: sdcar2010 时间: 2012-3-25 12:16
就算加入了B选项的assumption也不是充分的可以得出谁更可能超速的结论

B) is not a sufficient assumption, but a necessary assumption. That's the key.

当超速车=被ticket车时

This is wrong on two counts:
1) Only a fraction of speeding cars are ticketed.
2) The passage does not claim that either all the speeding cars are ticketed or the same fixed percentage of speeding cars are ticketed among both normal cars and car equiped with radar.

If something does not show up as a premise, you cannot take for granted that it is the case the author assumes. As test takers, we are asked to FIND assumptions, not to put assumptions into the author's mouth/mind.

作者: pirate舟 时间: 2012-3-25 12:37
关于1，题目也并没有明确说呀 Only a fraction of speeding cars are ticketed呀，这不算是 put assumption in author‘s mouth吗？
题目只是用了1、vehicles ticketed for exceeding the speed limit和 2、more likely to exceed the speed
就像我在2L说的，这里的区别只是 “在一个调查中，我们为了强调数量，说这段时间有多少多少辆车吃了罚单，而在说一个普遍的结论的时候，我们说某某车更容易超速。”
我并没有加入自己的assumption，这里完全可能说的all speeding cars are ticketed。而你认为的 Only a fraction of speeding cars are ticketed也是自己感觉出来的。

而且，如我在3L说的，如果认为Only a fraction of speeding cars are ticketed，用题目中的条件，加上任何一个选项，就连“ 装r的车比没装的更可能超速” 这个结论，更别提把它延伸到regularly的情况

作者: sdcar2010 时间: 2012-3-25 20:47
在调查中，被ticket车的就是超速车！而被ticket车和超速车的区别是，“被ticket车”是在调查中对超速车的称呼，而“超速车”则是指regularly情况下的。也就是说，调查中并不存在“没有被ticket的超速车”。

What LZ said above IS unsubstatiated assumption!

This passage is not about a group of policemen sitting at an intersection for three straight days and catching ALL the speeding cars and issuing a ticket for everyone of them . . .

This passage simply picks two somewhat related numbers from records and makes a conclusion.

If you agree that 题目只是用了1、vehicles ticketed for exceeding the speed limit和 2、more likely to exceed the speed
Then, you were wrong to say 就是用（‘装r的超速车’ 占 ‘装r的总车数’的比例）与（‘没装r的超速车’ 占 ‘没装r的总车数’的比例）来比较，就是用(33%*超速车)/ (3%*总车) 与 (66%*超速车)/ (97%*总车) 来比较
Because you added several assumptions, including B) to reach the above equation, and then you use your equation to conclude that the assumption B) is correct.

作者: pirate舟 时间: 2012-3-25 22:55
我的那个所谓的算式是来比较以得出 “谁更可能超速”这样一个结论。的确，如果要把33% 和 66%用上去就已经承认被ticket 和超速是一致的。

但是，而我这里最想关注的一个问题就是，如果按你的想法，仅仅根据题目条件和 B) ,请你告诉我是怎么可以的出“装r的车比没装r的车更可能超速” 这个结论，我们且把regularly放一边？？

你要比较谁更可能超速，就必须比较
（x*超速车)/（3%*总车) 与【（1-x)*超速车】/（97%*总车) 比较-------------x是超速车中安装了radar的比例

而我的意思就是，题目条件再加上 B) 给你，也是比较不了上面的大小的。。
因为结论其实包含了 “装r的比没装的更可能超速”和“regularly”两部分的，对吧？你连第一个都得不出来，就更不用去关注regularly了

所以，我为什么认为出题人这里的意思本身就是把被ticket车和超速车同等看待，就是因为当只有这样时候，才可能有前一部分的成立，然后答案是要我们选一个可以同时保证后一部分（即regularly）成立的选项。

作者: sdcar2010 时间: 2012-3-25 23:26
Necessary is different from sufficent.

LZ, you need to understand the difference between the two.

For the difference between sufficient assumption and necessargy assumption, here is an analogy:

Suppose you have city A and city B, separated by a river H. If there are multiple bridges over the river H, each bridge is sufficient but not necessary to connect city A with city B. What is necessary is that at least one bridge over river H is working.

If there is only one bridge over the river H, then that bridge is both sufficient and necessary to connect city A with city B.

If there there are two rivers C and D separate the cities A and B, and there is one bridge over C and many bridges over D, then the bridge over C is necessary (but not sufficient) to connect city A and B, while all the individual bridge over D is neither necessary nor sufficient to connect city A with city B. What is necessary is that at least one bridge over D is working!

作者: pirate舟 时间: 2012-3-26 00:02
sdcar2010 大牛，你的观点我在其他帖子里已经了解了，我也明白你在试图跟我说的问题。但是，我觉得在你的分析有一些问题，所以我也想请你抛开你之前的固有观点，看一看我所想表达的东西。可能之前我翻来覆去说了好多，有些杂了，我下面整理说一下我的重点：

首先，我把题目结论分为两部分来看待（1）装r的车比不装r的更可能超速（2）在（1）中的情况是regularly的

那么，我为什么认为“被ticket车”和“超速车”一致呢，有两个主要原因：
1、关于对结论（1）部分的论证：
我认为如果要有（1）这样的结论，一定是比较（x*超速车)/（3%*总车) 与【（1-x)*超速车】/（97%*总车) 才能得到的------------x是超速车中安装了radar的比例
但是，如果按照你的理解把“被ticket车”和“超速车”分开，那么x就永远未知，也就永远无法得出（1）中的结论，也就得不出整体结论。

那么也就可以认为出题人的本意就没有把上述两种车分开，正如我说的，题目没有明确说明 Only a fraction of speeding cars are ticketed，我并没有自己附加一个条件来说两者是一致的，而是出题人本来就没有把他们分开，是我们延伸思考以后认为 Only a fraction of speeding cars are ticketed。

2、如果姑且让我承认这两种车一致，根据题干中的条件我们就可以就可以比较两个比例，从而得出结论的（1）这个部分，而得不到（2）regularly这个情况。那么，现在的情况就是“我们有一特殊的结论，需要把它推广到普遍的结论”。
我想请sdcar2010 姑且承认这个情况，重新去看一下每一个选项，以及og对每一个选项的解释，你就会很清晰发现，og想说的其实就是这个意思。非常清晰。

所以，我在这里认为，出题人的本意就是 “被ticket车”和“超速车”是一致的。还请想请sdcar2010给出对应的反驳，特别是第1点。

作者: sdcar2010 时间: 2012-3-26 01:06
1、关于对结论（1）部分的论证：
我认为如果要有（1）这样的结论，一定是比较（x*超速车)/（3%*总车) 与【（1-x)*超速车】/（97%*总车) 才能得到的------------x是超速车中安装了radar的比例
但是，如果按照你的理解把“被ticket车”和“超速车”分开，那么x就永远未知，也就永远无法得出（1）中的结论，也就得不出整体结论。

Wrong. You still do not understand the difference between sufficient assumption and necessary assumption.

There are many roads to Rome. Some of them are the ONLY road (necessary). But using these roads ALONE cannot be sufficient for one to get to Rome. Nonetheless, these necessary roads are INDISPENSABLE.

Akin to the above analogy, a necessary assumption for the passage is indispensable for the conclusion to be drawn, but may not be sufficient when used alone to reach the final conclusion.

Once you understand the above explanation, you will understand why what you presented was wrong.

A rule of thumb: For a necessary assumption, the language is not strict, but broad and general, to cover many possible alternatives.
For a sufficient assumption, the language is strict and narrow, to narrow down to a single enabling scenario.

According to the passage, the numbers of 3% and 33% are just two numbers. The passage does not say both was obtained from the same "study." In fact the words like study or poll or the like are not mentioned in the passage! Like I said, both numbers are not from a STUDY with ALL the cars during a specific checkout period. If in doubt, ask a Chinese policeman for details.

Your equation is specific, requires A LOT of assumptions, thus, it may be sufficient, but not necessary.

作者: pirate舟 时间: 2012-3-26 01:43
According to the passage, the numbers of 3% and 33% are just two numbers. The passage does not say both was obtained from the same "study." In fact the words like study or poll or the like are not mentioned in the passage! Like I said, both numbers are not from a STUDY with ALL the cars during a specific checkout period. If in doubt, ask a Chinese policeman for details.
在这个题目当中，你的这个说法很有道理，如果我承认确实被ticket的车和超速的车不能看成一致的。
那么我不能理解的是，我们要如何从题目和B)中推出“有r的车比没r的车更可能超速” 这个结论，如果我们把regularly先抛开的话？

Your equation is specific, requires A LOT of assumptions, thus, it may be sufficient, but not necessary.
我的理解是，这个equation确实不是necessary，但是就题目的条件来看，这是我唯一可以推想的方向了，还是回到那个问题，我不知道要如何用题目条件+B)选项得出“有r的车比没r的车更可能超速” 这个说法？

作者: sdcar2010 时间: 2012-3-26 02:05
Necessary assumption. Use negation.

If you negate (B), you have:
Drivers who are ticketed for exceeding the speed limit are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed.

If that is the case, then for those drivers who have radar detectors and who got a speeding ticket, they are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed. This is in contrary to the conclusion of the stimulus -- Drivers who equip their vehicles with radar detectors ARE more likely to exceed the speed limit regularly than are driver who do not. So if you negate (B), the stimulus falls apart. Thus, (B) is the correct answer since it is necessary for the conclusion to be drawn.

作者: pirate舟 时间: 2012-3-26 02:36
两个问题：
1、Drivers who are ticketed for exceeding the speed limit are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed. ------>for those drivers who have radar detectors and who got a speeding ticket, they are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed.
Why? how did you bring the factor 'radar' inside this discuss?

2、So if you negate (B), the stimulus falls apart.
你这里的stimulus falls apart 具体指什么？是stimulus和conclusion falls apart吗？stimulus从来就没有和conclusion有过完整的逻辑联系呀。我想知道在你的整个推理过程中，是怎么运用题目although only 3 percent of drivers on Maryland highways equipment their vehicles with radar detectors, 33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them，这个条件的

作者: sdcar2010 时间: 2012-3-26 03:07
1) In the stimulus: 33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them. Therefore, 33% of those ticketed do have radar.
Since you like math, here comes the math: A = A1 + A2. If A is NOT more likely than B to do something and A comprises A1; then A1 is DEFINITELY not more likely than B to do something! That's called proper deduction.

2) stimulus = passage.

As to how to use the two cited numbers and reach the original conclusion in the passage (stimulus), that is not my concern because that is asking for an enabling condition to satisfy whatever has been said in the passage. My job is to find a NECESSARY assumption that must-be-true for the passsage (stimulus) to hold.

Nonetheless, the surposed logic which is used in the passage (stimulus) is that the 33% number is a true reflection of those drivers who are speeding on a regular basis. In other words, those who were issued a speeding ticket were not due to bad luck but due to their normal behavior. Choice B) is necessary for the above logic to hold.

作者: yiayia 时间: 2012-3-26 06:36
楼主为解释公式而加的assumption：超速车=被ticket车，是没有事实根据的。

如果楼主对3%和33%还纠结的话，我可以给一个解释：
撇开regularly, if drivers who equip their vehicles with radar detecters are not more likely to exceed the speed limit than are drivers who do not, then it should not be that33% percent of all vehicles ticketed for exceeding the speed limit were equipped with them.
在不考虑其他因素的情况下，如果装雷达探测器的车主不是更可能比那些没装的人超速(换句话说，就是装雷达对是否超速无影响或者甚至会降低超速)，那么装探测器超速人的比例应该不是33%左右（肯定远远小于33%）。因此原推论成立
注意我的逻辑推理顺序：
A=it should be 33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them.
B=drivers who equip their vehicles with radar detecters are more likely to exceed the speed limit than are drivers who do not.
如果if not B, then not A 成立
那么if A,then B 成立。

事实上，装雷达探测器的超速驾驶人能更好地规避被ticket的风险，因为他们能发现雷达！所有实际装雷达测速器超速的人超速的可能性比数据表现的更高。

作者: pirate舟 时间: 2012-3-26 14:42
sdcar2010,谢谢你的解释，同意。然后我又有没想通的地方的，再次请教，在你13楼的推理中： for those drivers who have radar detectors and who got a speeding ticket, they are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed. This is in contrary to the conclusion of the stimulus -- Drivers who equip their vehicles with radar detectors ARE more likely to exceed the speed limit regularly than are driver who do not.

我觉得前半部分的结论是没有一定contrary to 后面这部分的。因为在这里， drivers who are not ticketed 里面，有的装了radar、有的没装，那么我们依然没有充足的理由来比较装radar和没装radar 谁更可能超速，也就是说这里可能contrary to 也可能没有。

作者: pirate舟 时间: 2012-3-26 14:58
yiayia你好
撇开regularly, if drivers who equip their vehicles with radar detecters are not more likely to exceed the speed limit than are drivers who do not, then it should not be that33% percent of all vehicles ticketed for exceeding the speed limit were equipped with them.
在不考虑其他因素的情况下，如果装雷达探测器的车主不是更可能比那些没装的人超速(换句话说，就是装雷达对是否超速无影响或者甚至会降低超速)，那么装探测器超速人的比例应该不是33%左右（肯定远远小于33%）。

你这里就说不通呀。 1、首先结论中是，被ticket同时装雷达的，占被ticket车的33%，你这里就没有考虑到被ticket车和超速车的区别了。
2、再者，如果我们忽略区别，或者被 ticket的车有代表性，根据你说的 “(换句话说，就是装雷达对是否超速无影响或者甚至会降低超速)”，那么在被ticket车里面，装雷达的只用等于或小于50%就可以了

作者: sdcar2010 时间: 2012-3-26 20:35
If A=A1 + A2, B = B1 + B2; and A is not more likely to do somethi1ng than B; Then A1 is not more likely to do something than B2. Same logic!

作者: pirate舟 时间: 2012-3-26 21:04
for those drivers who have radar detectors and who got a speeding ticket, they are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed. This is in contrary to the conclusion of the stimulus -- Drivers who equip their vehicles with radar detectors ARE more likely to exceed the speed limit regularly than are driver who do not.

麻烦在上述这个推理之中对应一下A1，A2，B1，B2各自所指啊。。我对不上啊~~~If A=A1 + A2, B = B1 + B2; and A is not more likely to do somethi1ng than B; Then A1 is not more likely to do something than B2.
按照这个推论，A是指（装radar+被ticket），B是指（没被ticket的所有），A1指（装radar所有），B2指（没有radar所有）

作者: sdcar2010 时间: 2012-3-26 21:08
A = ticketed. B = not ticketed. 1 = with radar. 2 = w/o radar.

作者: pirate舟 时间: 2012-3-26 21:17
for those drivers who have radar detectors and who got a speeding ticket, they are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed. This is in contrary to the conclusion of the stimulus -- Drivers who equip their vehicles with radar detectors ARE more likely to exceed the speed limit regularly than are driver who do not.
If A=A1 + A2, B = B1 + B2; and A is not more likely to do somethi1ng than B; Then A1 is not more likely to do something than B2.
（A = ticketed. B = not ticketed. 1 = with radar. 2 = w/o radar.）

那么也就是，A1指ticketed 里面with radar的车，B2指not ticketed里面without radar的车
结论中比较的是1和2，并不是A1和B2 啊？？

作者: pirate舟 时间: 2012-3-26 21:23
for those drivers who have radar detectors and who got a speeding ticket, they are NOT more likely to exceed the speed limit regularly than are drivers who are not ticketed. This is in contrary to the conclusion of the stimulus -- Drivers who equip their vehicles with radar detectors ARE more likely to exceed the speed limit regularly than are driver who do not.

而且你的上述推论里面说的的是 A1 is NOT more likely to do somthing than B; then 1 is not more likely to do something than 2.
并能用If A=A1 + A2, B = B1 + B2; and A is not more likely to do somethi1ng than B; Then A1 is not more likely to do something than B2.来解释呀

作者: yiayia 时间: 2012-3-26 22:04
抱歉之前的解答，我想楼主是无意而为的，CDers聚在这里，只是单纯为互相帮助，没有义务一定要解答，保持互相探讨的精神是值得鼓励的，其他人解答的可能并不能令楼主信服，但请首先站在对方的角度来看待问题，而不是一味地推翻别人，维护自己的推理。

我不是NN，请允许我这个普通人来看待这个问题,叙述有点啰嗦，请见谅。
1.If drivers on Maryland highways equipment their vehicles with radar detectors are as likely as exceeding the speed than are drivers who do not, then the proportion all vehicles(both with andnot with radar detectors) ticketed for exceeding the speed limit should be the same,namely, the proportion of vehicles ticketed for exceeding the speed limit and with radar detectors among all the vehicles equals to the proportion 3% of drivers on Maryland highways equipment their vehicles with radar detectors among the all drivers on Maryland.
Unstated Assumption: a.whether equip with their vehicles with radar detectors will not influence the possibility of being ticketed.
b. One people drive a car.

However，the experience tells us that drivers use radar detectors to avoid being caught by the radar, and then avoid being ticketed. So let's make the argument more precise, the proportion of vehicles ticketed for exceeding the speed limit and with radar detectors among all the vehicles should be lower than 3%. But the data shows that 33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them, far exceeding the number we estimate. Thus, we can conclude that drivers who equip their vehicles with radar detecters are more likely to exceed the speed limit than are drivers who do not. The possibility of being ticketed for drivers who equip their vehicles with radar detecters is lower than the possibility of being ticketed for drivers who equip their vehicles without radar detecters. But the possibility of exceeding the limit for drivers who equip their vehicles are higher than than the possibility of exceeding the speed for drivers who equip their vehicles without radar detecters. Here is the logistic sequence.

作者: pirate舟 时间: 2012-3-26 22:34

抱歉之前的解答，我想楼主是无意而为的，CDers聚在这里，只是单纯为互相帮助，没有义务一定要解答，保持互相探讨的精神是值得鼓励的，其他人解答的可能并不能令楼主信服，但请首先站在对方的角度来看待问题，而不是一味地推翻别人，维护自己的推理。

啊~~~如果有语气冒犯的地方真是不好意思啊，yiayia，我真的没有故意要去和谁对着，或者一味就想推翻别人，我真的是出于希望找到处理这道题目的一个好的思路，再次抱歉。。其实我这几天简直是怀着一颗无比无比感动的心情，每天对sdcard提出我的看法，他每次都那么认真的给我解释，我的心已经早就被融化了。！。！。。当然对于yiayia肯花自己时间来为我做出解释，我又何尝不是同样的心情。。。你说你不是NN，那就是在戏谑同学我拉，我始终努力追随你们的脚步，希望可以考个好分数，在gmat的世界里，你们都是小弟的老师呀！
sorry，你对于本题的进一步分析我还没开始看，忍不住要先舒一下情，一来化解yiayia对我的误会，再就是对大家表示我的深切感激啊~~

作者: undefeatedxk 时间: 2012-7-9 19:08
还是同意LZ的不论解释多么合理如果不符合OG的解释的话都没用，要不也不用刷OG了。解释里面说的就是gap在于particular example to generalization，就像实验数据和实际情况一下。

作者: sami244 时间: 2012-7-26 17:56
刚看到一个解释比较简洁

B选项减少了无ticketed司机超速的可能性，否则没有装RD的司机可能超速了而没被开ticketed(特例)，这样比较就没有意义了

感觉这个比较好理解，也满足了og的解释

作者: shunshun2008 时间: 2012-7-28 20:27
刚刚重新看完这题，自己的分析思路和楼主类似，正是因为如此，我觉得这种分析太绕了！起码要五分钟啊！我觉得楼上说得很对，关键在于如何用一个假设把例子转为一般情况。装雷达被开罚单与装雷达没被开罚单的比重较之没装雷达被开罚单与没装雷达没被开罚单的比重大，我们可以得到貌似装雷达更容易比不装雷达被开罚单，我们再加入以下假设：被开罚单的比没被开罚单的更经常性地超速，那么我们可以说装雷达比不装雷达更经常性超速。也就是题目的结论。

作者: eb1forever 时间: 2012-7-30 23:53
顶大牛sdcar

作者: chelsea1211 时间: 2014-12-12 16:43
贴一个Manhattan的解释：来自Stacey：
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 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.

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.

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.
RON--the existing problem with the passage is that it conflates "people who are ticketed for speeding" with "people who speed regularly".
since these two things are, in fact, not the same, we need an assumption that the group of people ticketed for speeding actually represents people who speed more often.
basically, this argument is treating X (= people ticketed for speeding) as if it were the same as Y (= people who actually speed all the time).
this X and Y are not necessarily connected, so you need an assumption that connects them. the correct answer does this job.
you would need the same type of assumption if, e.g., the premises of the argument talked about "people convicted of crime X" but the conclusion talked about "people who have committed crime X".
if this were a strengthening/weakening problem, then choice (a) would be a strengthener; if people driving with radar detectors were actually less likely to be caught and ticketed, then the 33%/3% discrepancy described in the passage would actually take on even more significance.
an assumption is a statement that is REQUIRED in order for the argument to work. (if you have a statement that considerably strengthens the argument, but isn't actually REQUIRED, then it's not an assumption. period.)
this assumption treats the population of drivers who are ticketed for speeding as a reliable representation of the general population of speeders. although this may seem "obvious" to you, it is still a required assumption!

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