PT 59 Sec 2 LR1 Question 20 Forum

[birchum]

For this question I was stuck between B and D. I just can't wrap my head around why B is incorrect. Any help would be appreciated.

[nmare]

I would say because the field inspectors were JUST AS LIKELY to choose defective over non-defective. This does not provide a flaw being that if they were just as likely to choose defective over non-defective, than they were not out looking to test ONLY defective items. Answer choice (D) however suggests that they were going out of their way to test only items they suspected to be defective, thus providing the flaw in the argument.

[Campagnolo]

Any other thoughts on this? I still can't make it work for myself.

[Obelisk18]

This one gave me trouble too- I changed the answer twice but ultimately went with D. Here's why. The investigator claims they manufacturer has violated the contract because the field inspectors found more than 20% defects when there were supposed to be under 5%. Imagine there were 100 samples. What would choice B mean, literally, in that case? That the investigator presumed that the field inspector had chosen 50 defective samples and 50 non-defective samples. Is that what the investigator is presuming? Not at all. He's presuming that the sample chosen is representative of the overall product line. I'm pretty sure that this is a different take on the old "proportions vs. absolute numbers" trick. The phrase "X is just as likely as Y", when there are only two choices, means "there's a 50% chance of X and a 50% chance of Y". Again, this doesn't capture his assumption. And here's another problem, even if you misread B- the investigator isn't necessarily assuming that it's an exactly representative sample. The difference between 5% and 20% is pretty substantial. The field inspectors could have oversampled the defective items by 100% and the investigator would have still been justified in his conclusion. In order to undermine his contention, you'd need an AC that showed not only that defective items were oversampled, but that they'd been sampled inappropriately, in a way that undermines the possibility of any conclusion. Even if you took B to mean "presumes that the field investigators as many defective items, proportionally, as non-defective items, proportionally" it wouldn't do the trick.

[Campagnolo]

That makes sense. I mistakenly read answer choice (B) as: presumes the inspectors have no bias when selecting items for testing. What (B) really says is: It's a coin toss whether the inspectors send in a defective item or a non-defective item, which would in turn mean that the contract is violated.

I finished the section with more than 4 minutes at the end, and sat there puzzling hopelessly. I think I have it now.

Thanks!

[hyakku]

Holy shit I thought I was the only one that did this. I was especially pissed because recently I've been an assassin on 50/50 chances, but I couldn't get that for shit until I started thinking about it like another poster said. Now that you all confirmed it I'm glad, I think this is going to be a question that becomes more and more prevalent (noticed some easier variants of it after that on 63 and 62) so it's definitely a rationale worth learning.