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标题: CR Strategy Guide 5th Ed [打印本页]

作者: sdcar2010 时间: 2012-6-9 20:53
标题: CR Strategy Guide 5th Ed
CR Strategy Guide 5th Ed
Chapter 5 (strengthen and weaken), Question #8 (Ethanol)
Page 179-182

Ethanol, a fuel derived from corn, can be used alone to power cars or along with gasoline to reduce the amount of gas consumed. Unlike gasoline, ethanol is easily renewable since it is primarily converted from the sun's energy. Moreover, compared with conventional gasoline, pure ethanol is a cleaner-burning fuel. To save energy and reduce pollution, many individuals advocate the increased usage of ethanol as a primary fuel source in conjunction with or in place of gasoline.

In evaluating the recommendation to increase the use of ethanol, it would be important to research all of the following EXCEPT:

(A) Whether the energy required to grow and process the corn used as fuel is greater than the amount of energy ultimately produced.
(B) Whether more energy is saved when using ethanol in conjunction with or in place of gasoline
(C) Whether ethanol is as efficient a fuel as gasoline
(D) Whether it is possible to produce more ethanol than is currently produced
(E) Whether the process of growing corn for fuel would result in as much pollution as does the production of conventional gasoline

The biggest problem I have with choice D is that it does not COMPARE EtOH with gas. B, C, D do. A is related with the use of EtOH as a fuel.

Second, let's say if the answer to D is yes and see if that would help us decide. Since it is known that EtOH can be produced from petroleum oil (remember our middle school chemistry lessons?), even if more EtOH is produced from petroleum, it will not save energy or reduce pollution. But if more EtOH is produced from corn, definitely it is possible to save energy or reduce pollution.

Third, let's say if the answer to D is no and see if that would help us decide. We will fall into the same traps I described above since all the total EtOH may not be increased, the portion of EtOH produced from corn vs. that from petroleum oil might be changed. Again, we would not know for sure whether the recommendation will work or not with a NO to D.

In sum, D will not help one decide on the validity of the recommendation in the passge. I agree with Babybearmm, D) should be considered as a possible correct choice, together with B).

B) is a correct choice as well.

作者: sdcar2010 时间: 2012-6-10 01:31
However, if GMAT igores the fact that EtOH could be produced from petroleum, and claims that EtOH is totally produced from corn or other renewable source, then D) would not be the correct answer choice for this question. That would leave B) as the only good choice.

作者: babybearmm 时间: 2012-6-10 03:35
Hi sdcar, thanks a lot for your analysis.
Honestly I did not ever think of this issue: EtOH can be produced from petroleum (omg I feel embarrassed that I was in Chem Dept. in my undergrad

)... But yes, that's a great point! If the production of EtOH tells us nothing about its energy or environmental impact, then Choice (D) is a non-issue.

Excuse me but I cannot get this "if GMAT igores the fact that EtOH could be produced from petroleum, and claims that EtOH is totally produced from corn or other renewable source, then D) would not be the correct answer choice for this question."
If EtOH can only be produced from renewable source, then ... how can the answer to Choice D (Yes/No) help evaluate the plan?
I still think Choice D is irrelevant.... "possible to produce more than is currently produced" does not tell us the availability of the EtOH, since we do not now how much is currently produced. In mathematical term, I think what we care is the X(final), not deltaX (since we do not know X0).

Your insight is greatly appreciated.

However, if GMAT igores the fact that EtOH could be produced from petroleum, and claims that EtOH is totally produced from corn or other renewable source, then D) would not be the correct answer choice for this question. That would leave B) as the only good choice.

-- by 会员 sdcar2010 (2012/6/10 1:31:14)

作者: sdcar2010 时间: 2012-6-10 21:45
My reasoning was based on the the following constraint: In evaluating the recommendation to INCREASE the use of ethanol . . .

To do that, the production of EtOH has to be increased in the future. Therefore, the potential to make more EtOH is relevant to the proposal.

作者: babybearmm 时间: 2012-6-11 11:34
Oh i get it. Thanks sdcar guru

My reasoning was based on the the following constraint: In evaluating the recommendation to INCREASE the use of ethanol . . .

To do that, the production of EtOH has to be increased in the future. Therefore, the potential to make more EtOH is relevant to the proposal.

-- by 会员 sdcar2010 (2012/6/10 21:45:00)

作者: yiayia 时间: 2012-6-12 13:09
Well, I have a long time not to do some reasoning practice. If I have stated any wrong, please correct me.

When I first read the choice B. I was quite confused. What does B compare? I thought it was comparing the use of Ethanol mixed with petrol and the only use of petrol. That is to say, the choice B can be replenished like this: whether more energy is saved when using ethanol in conjunction with or in place of gasoline than using only gasoline. Note there is an "or" between the words. It has nothing to do nothing to do with the increased usage of ethanol.

The analogy between stock A and stock B is very nice(CFA!haha). But note before your apply it, you have to ensure there is no synergistic effect. It will make it possible that even though ethanol is costing more energy the mixed gasoline will be more efficient!

Choice D reasons like this: it must be possible to produce more ethanol than is currently produced. Then it can be used more to be the fuel. I reckon that considering the import or the difference of production and consumption is reasonable somehow but still out of scope.

Therefore, the most important element to analyse the problem is "To save energy and reduce pollution" and "increase the use of ethanol".

作者: babybearmm 时间: 2012-6-12 16:53
"you have to ensure there is no synergistic effect"
Brilliant point! Now I feel that GMAT logic does not allow "extrapolation", which is valid only if the relationship is linear or alike. GMAT would consider an "extrapolation" out-of-scope.

For Choice D, looks like I myself made out-of-scope assumptions in evaluating this choice...

Thanks yiayia! I'm clear now.

作者: 有理想没有钱 时间: 2012-6-15 05:17
Hi Baby,
For the answer B, we can easily differ them between the conclusion involved the INCREASED use of ethanol and the use of ethanol. Thus, this kind of false, using the dot to represent the area, always showed in the Gmat CR question. I have scaned all the answers they proposed in this thread and to some extent agreed with them, But you know that when you take the real test, you dont have so much time to think in that way, thus, i think that you'd better to aware whats the problem in answer B. We can find so many answers using the pot to represent the area in the og is definitely out of scope. Hopefully, you can acuire this kind of ability that is the knowledge you need to learn for your test.

For the answers D. Frankly, i chose it as the right answer because i think the argument just talk about the use of ethanol or gasoline, However, the production of them is irrelevant. This flow is actually right in our mind, but, comparing the B and D, we can find that D at least has a liitle realtionship affecting the conclusion in argument. However, answer B, using the pot to represent area, whatever you use the negation method or some other methods, you cannot negate the conclusion right.

In short, using pot to represent the area just like the comparison between beautiful girl and girl when you want to show the advantage of the beautiful girl. There is no significant relationship. Right?

Finally, Doing this kind of question, we should aware that whats the problem in each answer choices, and then compare them and recall the typical false flow in OG, thus, at last we could choose the right answer OG LIKE....

Hopefully it is useful for you.
Good luck to your future exam....

作者: yakev6 时间: 2012-9-10 18:47
Wow!!! how brilliant discussion here. So insightful
Talk about my understanding of evaulation, evaulation is a consideration in that the different answer to the question will have totally different logic level driving force. The answer "yes" will strengthen the conclusion and "not" will weaken it.

Weaken/Strengthen can be qualitative (totally ensure--100% certainty or destroy--0% certainty,) or be quantitive, or say posibility level related, (1% certainty enhanced or 1% certainty reduced). From this point of view, D is relevant, because the Y/N diversity have different posibility level strengthen/weaken effect.

if Yes, the posibility to increase the use of ethanol is enhanced.
if No, the posibility to increase the use of ethanol is reduced.
And the posibility to increase the use of ethanol is related to the recommendation.So D is ok for me.

For (B) Whether more energy is saved when using ethanol in conjunction with or in place of gasoline,
More is wrong for me.

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