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

pirate舟

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

chelsea1211

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!

eb1forever

顶大牛sdcar

shunshun2008

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。

sami244

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

undefeatedxk

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。

pirate舟

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~~

yiayia

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.

pirate舟

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

pirate舟

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？？