#20 - Quality control investigator: Upon testing samples

[g89]

Section 2 #20 (Quality control investigator)
I understand why D is correct, but I'm not really sure why B is wrong. In believing that the sample (which was 20% defective) was representative of all of the items, the investigator is assuming it is a random sample. And that's what B states -- assuming the sample to be random would mean he presumed that the inspectors were just as likely to choose defective and nondefective items.

Thank you!!!!

[Steve Stein]

Thanks for your question. Investigator can't presume that the inspectors were just as likely to choose a defective item as a non-defective item—if defective and non-defective were exactly equally likely to be chosen, that would lead to a defect rate of 50%.

[beniakc]

#20
How is D correct? I see B,C,D and E as all being possibilities.
C and E roll together (basically saying that are the problems coming from 1 plant and you didnt visit any others or did you make a trip to all plants). I think B and D go together. Could they have been in a plant where every item produced was defective or did they make trips to all plants? I never considered A.

With B,C,D and E all being close, is it just a matter of wording that I am missing?

[Steve Stein]

For that one, the investigator is basically assuming that the selection sent by the field inspectors has the same defect percentage as the supplier’s overall production. Answer choice D provides exactly that: the author overlooks the possibility that the field inspectors’ choices are biased.

The problem with B is that the author does not presume a 50% defect rate. The problem with C is that we don’t know whether the field inspectors went to only a few sites. Maybe they went to every site and took a perfectly random sample. The problem with E is that there is no such presumption regarding equal numbers of visits.

Let me know whether those are clear—thanks!

~Steve

[beniakc]

I see exactly what you are saying. I have noticed that, in taking tests or prac sessions, when I come across answers that jump out at me as correct, I have been pushing them aside under the presumption that I could not have come to the conclusion that quickly, thus I feel like that answer is wrong. I did that several times in this test today. Each one cost me a correst answer.

Any ideas?

[Steve Stein]

I'd say that's one of the hazards of getting comfortable with the test and starting to see the patterns. Thats an important selling point for taking practice tests and sections. Take note of the kinds of questions that you see right through; as you see and quickly conquer more of those, you should also increase your confidence when, in some cases, the right answer choice is immediately clear.

[PowerSteve]

Regarding question number 20 from the first logical reasoning section of December '09, I understand why choice D is the best answer, but does C make some sense as well? The stimulus explicitly states that the samples came "from various manufacturing locations." I can imagine that there are 100 manufacturing locations in total and that the samples are coming from 10 of them. Certainly then the samples are coming from various locations, and yet it could be possible that at least one of those manufacturing sites produces a significantly higher percentage of defective items. Thus, the argument is overlooking, as choice C states, "the possibility that a few of the manufacturing sites are responsible for most of the defective items."

~Steve

[Adam Tyson]

I think the author's intent here was to use "various manufacturing sites" to suggest that it's not a local problem at one site, Steve, but I think you make a very good point, and I can see making that argument (and can even see that being a real-world solution in a case like this). This is one of those occasions when I am going to rely on something I rarely turn to - the instructions for the test itself. They tell us to pick "the best answer" rather than "the correct answer". While we can imagine a situation where C might be right, the very fact that we have to create that scenario to make the answer work tells us that while it might be a good answer, it's not the best one. D makes more sense, and it takes no "what if" brainstorming to make it work.

In the SAT world we talk about "kind of" answers - that's where a student looks at an answer and says "that kind of works." We tell students to reject those answers, because when we start saying "kind of" we're actually helping the test makers out by giving them the benefit of the doubt. We're helping them to make an argument for one answer choice over another. Don't help these guys - they are the enemy! We want to defeat them, not give them aid and comfort by making their wrong answers right. I think that same tactic applies here - don't try to improve an answer choice, but take it as it is and decide if it's the best one without having to help it.

Hope that helps!

Adam M. Tyson
PowerScore LSAT Inst

[PowerSteve]

Thanks Adam. That problem still kind of upsets me. The test makers could have very easily stated "from all of the manufacturing locations" instead of "from various manufacturing locations." This would have then taken away the possibility alluded to in choice C. Instead, they kept that possibility alive and yet did not have the quality control investigator address the possibility (hence, overlooking it). Perhaps they wanted to make choice C look more attractive, but I think they went too far. If instead of saying "possibility" they used a word like "probability," then I'd be OK with dismissing choice C, but "possibility" is so weak. Anyway, I'm just venting here at this point - you don't need to bother responding! I do understand what you wrote, and as I mentioned in my first post, I also understand why choice D is the best answer. I'll just have to get back at these test makers by destroying their test on June 11th

[Basia W]

Good afternoon,

I had difficulty with the question, and I chose the wrong answer C. I was unsure which one of the answer choices presented the flaw in the argument, and would greatly appreciate your approach on how to attack this question!

Best,

Basia