CR Strategy Guide 5th Ed "Ethanol"

[thulsy]

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



Correct answer is (B).
I incorrectly chose (D) for this question. After reading the solution, I still have the following inquiries:

1. Regarding D
The conclusion is "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."

I have learned from the Verbal Foundation book that the infinitive ("to save ...") in the conclusion is very important, and that we should stick to the proposed purpose when evaluating the argument.

Having this consideration in mind, I thought Choice (D), which is about the possibility of producing ethanol, is out of scope, since it addresses neither saving energy nor reducing pollution.

Even if we consider the feasibility of the plan, the availability of ethanol is not equal to "possible to produce", since we may get ethanol by other means, such as import, or if new technology comes out - who knows.... So I think the question asked in Choice (D) is irrelevant.

Moreover, I don't agree with the explanation "If we cannot produce any more ethanol, then how can we increase the usage?"
(D) says "than is currently produced".
However, we do not know how much is currently produced. In order for the question asked in (D) to be meaningful, we need additional assumption: the ethanol currently produced cannot meet the future demand for the plan.
but what if currently the ethanol production has surplus (i.e. ethanol production >> ethanol consumption)? If this is the case, then even if we cannot produce more ethanol than now, the plan is still feasible - we can consume the surplus ethanol that we already have now.

(I was taught not to make additional assumption to justify the answer choice, and thus I doubt Choice D, whose justification requires additional assumption.)

What went wrong with me? Should I continue paying close attention to the infinitive (expressing purpose of the plan) in the future?

2. Regarding B:
I understand the explanation that "the conclusion makes no distinction between these two methods", but what I thought was quantitative:
the intuition is, let's say Stock A is more profitable than Stock B. Then in a portfolio that consists only Stock A and Stock B, the heavier weight that Stock A carries, the more profitable is the portfolio. So we can make a recommendation: "advocate the increased weight of Stock A in conjunction with or in place of Stock B".

Here,
method #1: "using ethanol in conjuction with gasoline", which means a portion of gasoline is replaced by ethanol
method #2: "using ethanol in place of gasoline", which means all the gasoline is replaced by ethanol

If the result is method#1 saves no more energy than method #2, that means the more ethanol is used in place of gasoline, the more energy-saving. then this result definitely strengthens the argument that "increased usage of ethanol" will save energy.

If otherwise, i.e. method #1 saves more energy than method #2, then that means ethanol is not as energy-effective as gasoline, and then the conclusion will die.

If my above reasoning is correct, then Choice B should be helpful in evaluating the plan. Please correct me if I am wrong.

Thanks in advance.

[thulsy]

"The most common trap answers typically involve making some kind of irrelevant distinction or comparison." (page 115)

Dear Instructor,
I have some confusion here regarding how this principle applies to Choice (B). I made the following analogy:

Argument: Since study is good, those who did not study at all should either study a little or study a lot.

Choice (B): "Study a lot" is better than "study a little".

Does Choice (B) strengthen the argument?

I think it does. Because according to B, the more one studies, the better. Therefore, study some amount is better than no study at all. So the argument is strengthened.

Any comments? Thanks.

[jlucero]

1. Regarding D:

I see your point that someone who thinks D is making an assumption that we don't currently produce enough ethanol to support the plan advocated in the argument. But by saying that we have enough ethanol currently in order to meet demands is a rather large assumption itself. You might be able to skirt this issue by saying that we currently have large ethanol reserves built up or that we would be able to shift ethanol usage from another industry, but those produce problems themselves: what happens when we use up our supply of ethanol? What will those other industries use in place of ethanol? If we want to replace a major resource with renewable ethanol as a "primary fuel source", it's very relevant that we have enough ethanol to be able to make this switch. Thinking that we produce enough of this ethanol and that it's just sitting around somewhere is just too big of a leap in logic.

2. Regarding B:

"Ethanol, a fuel derived from corn, can be used alone to power cars or along with gasoline to reduce the amount of gas consumed."

The initial statement tells us that ethanol by itself or an ethanol/gasoline mixture will each reduce the amount of gas consumed. As you said, the conclusion makes no distinction between these two things. As long as each one saves energy, it's a win for ethanol.

But your logic in saying that if an ethanol/gasoline mixture was more fuel efficient than just ethanol, the conclusion would fail is wrong. Maybe ethanol isn't a great fuel on its own. Maybe it needs some gasoline to maximize its energy potential. A stock portfolio is not a great analogy for this because it doesn't show how a mixture can sometimes be better than one vs the other. A better analogy might be a diet. If vegetables are also healthy for you, then eating a mixture of meat and vegetables can't be healthy for you? A mixture might optimize the benefits of each part. Whether I eat only vegetables or vegetables along with other foods, it's still better than me not eating vegetables. Ethanol can save energy whether it's better in a mixture or by itself.

[jlucero]

Thulsy-

The same point about vegetables applies to your argument- whether you study a little or a lot, that's not the point your argument is trying to prove. It could be true. But it could be not true- maybe students do best after only studying a little.

Your conclusion is that not studying is worse than either studying a little or a lot. Comparing studying a little vs a lot is an irrrelevant point to the main argument. And jumping from ' "Study a lot" is better than "study a little" ' to ' the more one studies, the better ' is a large jump in logic. Maybe there's something in between these two parts: "studying quite a bit" that's better than either one. Two points can make a line but two points can also be part of a parabola too!

[thulsy]

Hi Joe,
Great explanation! I get it. Thanks a ton! :)
I especially like your vegetable analogy. Now it seems to me that in GMAT CR, we are not automatically allowed to do linear regression and make extrapolation, because data point outside the range is considered "out of scope" (no extrapolation) and linear regression itself requires unjustified additional assumption (e.g. no synergistic effects).

[jlucero]

Awesome!

[imhimanshujaggi]

Hi Instructors,

I have a doubt with choice B, request you to please clarify my doubt.
Choice B says that Whether more energy is saved when using ethanol in conjunction with or in place of gasoline.

How do we make sure that the "Two paths" should be -

a) checking whether more energy is saved using ethanol alone vs whether more energy is saved using ethanol in conjunction

and NOT

b) checking whether more energy is saved using ethanol in conjunction with or in place of gasoline. Answer to this question - Yes or No can strengthen and weaken choice.

Please clarify.

Thanks

[jnelson0612]

Hi Instructors,

I have a doubt with choice B, request you to please clarify my doubt.
Choice B says that Whether more energy is saved when using ethanol in conjunction with or in place of gasoline.

How do we make sure that the "Two paths" should be -

a) checking whether more energy is saved using ethanol alone vs whether more energy is saved using ethanol in conjunction

and NOT

b) checking whether more energy is saved using ethanol in conjunction with or in place of gasoline. Answer to this question - Yes or No can strengthen and weaken choice.

Please clarify.

Thanks

Hi,
I confess that I'm not fully understanding your question. Answer choice B is the answer that DOES NOT matter to whether this suggestion is a good one. In the two options you put above, option a) matches answer choice B. Your option b) is already stated by the passage: energy is saved when ethanol is used, either by itself or to replace some gasoline. Please take a look at Joe's excellent explanation earlier in this thread regarding B.

[liwh_gd]

could someone please explain why choice C is wrong?

[jnelson0612]

could someone please explain why choice C is wrong?

Sure. Let's look at the relevant parts of the argument again, and let's remember that we're trying to cross off everything that IS relevant to consider.

Conclusion: "To save energy and reduce pollution, use ethanol as a primary fuel source in conjunction with or in place of gasoline." In other words, only use ethanol for fuel or use it with a little gas.
WHY?
Premise: Unlike gas, ethanol is easily renewable and pure ethanol is a cleaner-burning fuel then is gas.

So all of these answer choices except one is getting at an assumption we need to make to get from the premise to the conclusion.

Let's look at C):
(C) Whether ethanol is as efficient a fuel as gasoline

That seems relevant! Remember, our goal is to save energy and reduce pollution. Consider the fuel efficiency of cars. If one gallon of gas can make your car go 50 miles, and one gallon of ethanol only propels your car one mile, I'd have to use 50 gallons of ethanol to get the same performance. That certainly won't save energy! Also, even if ethanol is cleaner burning than gas, we probably will have more pollution from burning 50 gallons of ethanol compared to one gallon of gas.

[liwh_gd]

Thanks for your wonderful explanation! Jamie!

Now I realize that "efficient" is not equal to "save energy"!

[jnelson0612]

Thanks for your wonderful explanation! Jamie!

Now I realize that "efficient" is not equal to "save energy"!

Great to hear! You are welcome. :-)

[supratim7]

Conclusion: "To save energy and reduce pollution, use ethanol as a primary fuel source in conjunction with or in place of gasoline." In other words, only use ethanol for fuel or use it with a little gas.

Where does "little gas" come from?
I figured the conclusion as "Increased usage of ethanol or ethanol+gasoline (A) will save energy/non-renewable energy/gasoline (B) will reduce pollution".
In the conclusion "will save energy/NRE/gasoline", I don't see any mention of "will save LOT OF energy/NRE/gasoline". Hope this interpretation is fine.

If it is, then we can evaluate "Choice C: Whether ethanol is as efficient a fuel as gasoline" in following manner (2-path approach)

Situation 1: "ethanol is as efficient as gasoline"
leads to "either less/more/as much ethanol than/as gasoline in fuel tank or no gasoline at all"
leads to "will save energy/NRE/gasoline".
Strengthens conclusion.

Situation 2: "ethanol is NOT as efficient as gasoline"
leads to "more ethanol than gasoline in fuel tank"
STILL leads to "will save energy/NRE/gasoline".
Arguably, lesser energy/NRE/gasoline savings than Situation-1, but this will save SOME amount of energy/NRE/gasoline. Strengthens conclusion.

Hope my reasoning is OK; pls help out.
Many thanks | Supratim

[jnelson0612]

Conclusion: "To save energy and reduce pollution, use ethanol as a primary fuel source in conjunction with or in place of gasoline." In other words, only use ethanol for fuel or use it with a little gas.

Where does "little gas" come from?
I figured the conclusion as "Increased usage of ethanol or ethanol+gasoline (A) will save energy/non-renewable energy/gasoline (B) will reduce pollution".
In the conclusion "will save energy/NRE/gasoline", I don't see any mention of "will save LOT OF energy/NRE/gasoline". Hope this interpretation is fine.

If it is, then we can evaluate "Choice C: Whether ethanol is as efficient a fuel as gasoline" in following manner (2-path approach)

Situation 1: "ethanol is as efficient as gasoline"
leads to "either less/more/as much ethanol than/as gasoline in fuel tank or no gasoline at all"
leads to "will save energy/NRE/gasoline".
Strengthens conclusion.

Situation 2: "ethanol is NOT as efficient as gasoline"
leads to "more ethanol than gasoline in fuel tank"
STILL leads to "will save energy/NRE/gasoline".
Arguably, lesser energy/NRE/gasoline savings than Situation-1, but this will save SOME amount of energy/NRE/gasoline. Strengthens conclusion.

Hope my reasoning is OK; pls help out.
Many thanks | Supratim

"little gas" comes from the bolded part here:
"use ethanol as a primary fuel source in conjunction with or in place of gasoline"

"primary fuel source in conjunction with . . . gasoline" means that ethanol will be the majority of the fuel and that you will have a minority of gasoline, hence "little gas".

As for as your conclusion, that is fine. We don't have to assume that the switch to ethanol will save a HUGE amount of energy/NRE/gasoline but the savings should certainly be enough to make it worth our while to make the ethanol in the first place. In other words, the savings should be moderate or more.

I guess I'm not sure if you have a question or if you are just laying out your own thought process here. Let us know if there is more clarification you need.

[acct4gmat]

Hello all,

From the above explanations, I understood that B is right as it is irrelevant to compare ethanol saved in cases 1) when using ethanol in conjunction with 2) in place of gasoline.
I am OK with it but my problem is that I misread the option B. I thought for comparing two cases that too with more , than should be used..Something such as "Whether more energy is saved when using ethanol in conjunction with than in place of gasoline".

If my understanding of using more is wrong, could you please throw some light on the proper usages of "more".

Thanks a ton in advance.