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 kaylinamey
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#96996
Hello!

I thought that E was wrong because you would have to use outside information to know that environmental pollution can cause cancer. Can someone please explain why this thought process is incorrect?
 Rachael Wilkenfeld
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#97056
Hi kaylinamey,

For a weaken questions, we don't need to know that environmental pollution causes cancer. We just need to know if it is a potential alternate cause for the higher cancer rates. The stimulus suggests that fat intake causes cancer. If there was something else present that could also have caused the high cancer rates, that would be a potential alternate cause. Our answer choice doesn't have to show that environmental pollution was the cause of the cancer rates. It just has to show that it's a possible alternative explanation.

Hope that helps.
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 kaylinamey
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#97296
Thank you Rachel! That did help :-D

I just ran into another question on Test 30 about rattle snakes that was similar. I had to find the alternate cause in order to find the correct answer. It was a Necessary Assumption question. When should I know to find the alternate cause in order to weaken or find the flaw in the question?
 Luke Haqq
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#97322
Hi kaylinamey!

Happy to address your question. You ask:

When should I know to find the alternate cause in order to weaken or find the flaw in the question?
You should always be looking out for things like alternative causes that might weaken or be flaws in a given question. Of course, logic games are an exception since one doesn't encounter those types of questions on games. But it's generally always worthwhile to do on any reading comprehension and logical reasoning questions. Upon reading through a given stimulus in logical reasoning, you also might find that there is no conclusion. This is common for the must-be-true question type. In that case there isn't an argument to weaken. But you can still be ready to pre-phrase flaws or assumptions on each question, even if they turn out not to have any. Pre-phrasing these things is an important strategy that keep one engaged and also can help one get through answer choices more quickly.

You also mention a question about rattlesnakes, which I believe is question #22 from practice test 30. The conclusion of this stimulus comes at the outset: "The folktale that claims that a rattlesnake’s age can be determined from the number of sections in its rattle is false." Why does the author claim this? The author explains that its rattle does contain indications of the number of times that its molted, but that pieces fall off because it is brittle, making it difficult to determine age.

After reading this stimulus, I was left with uncertainty about how molting refers to age. That uncertainty could potentially be because of a flaw or unstated premise, so it seems worth trying to pre-phrase something in light of it. Without keeping an eye out for flaws and assumptions, I might instead have inadvertently made some connection between age and molting myself--perhaps rattlesnakes molt annually, for example. Each notch in its rattle would then indicate a year. Or perhaps they molt monthly.

In looking at the answer choices, answer choice (A) might have been tempting if I hadn't been thinking about this ambiguity as a potential flaw, but nothing in the argument requires the rattle to indicate age according to years, rather than some other measure like months or weeks. Answer choice (E), however, states,

Rattlesnakes molt as often when food is scarce as they do when food is plentiful.
To test if this is a necessary assumption, we can apply the two steps of the Assumption Negation technique. First, we negate the statement:

Rattlesnakes [do not] molt as often when food is scarce as they do when food is plentiful.
Second, we ask if the argument falls apart with this negated statement put back in, in which case it is a necessary assumption. The argument would fall apart if we added this statement, since this would suggest that the number of times a rattlesnake molts isn't constant but rather varies and fluctuates based on their food source; if that's true, then the rattle can't be used to judge age. The Assumption Negation technique therefore confirms that (E) must be the correct answer.
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 CristinaCP
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#105150
Hi Powerscore!

I thought this question was very similar to a question from PT 79 (S1, Q21), which is similarly assuming a causal relationship from a correlation. For #21, the answer choice which proposes another correlation (and potential cause) is wrong. Someone explained why it’s wrong by saying that even if there’s another correlation suggesting an alternate cause, the original factor proposed by the stimulus could still be a potential cause. I used that same reasoning to eliminate [D] for this question. Even if those countries with high avg fat intake also have environmental pollution, high fat intake could still be a cause of cancer. So why is the “alternate cause” weakener wrong for the question from PT 79 and right for this question? Is it wrong for PT 79 because it’s just “less right” than the credited answer?
 Robert Carroll
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#105219
CristinaCP,

In the thread for PT 79 (S1, Q21), it's pointed out that the supposed "alternative cause" isn't alternative at all - it's actually an additional correlation that is perfectly consistent with the author's conclusion. That's why it doesn't weaken. Alternative causes must be in fact alternative in order to weaken an argument.

Consider this argument:

"Everyone who got into a fatal accident on Route 79 last year was driving over the speed limit. So speeding causes fatal accidents."

Consider an answer that's supposed to weaken this:

"Every person who got into one of the fatal accidents was driving a car that was in fifth gear."

Is being in fifth gear really an alternative cause? Cars in fifth gear will tend to be doing higher speeds. So this is an additional correlation, but it's pretty consistent with the conclusion. The same issue existed in the other question you talked about.

Returning to the topic of this...topic, environmental pollution bears no plausible connection with fat intake. It's thus an alternative cause that is not consistent with the original conclusion. That's why it works. It's truly alternative - to the extent that some of the cancer is caused by pollution, it's not thereby also caused by fat intake.

Robert Carroll

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