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# Photovoltaic power plants produce electricity from sunlight.

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Photovoltaic power plants produce electricity from sunlight. [#permalink]

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15 Feb 2008, 15:02
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Photovoltaic power plants produce electricity from sunlight. As a result of astonishing recent technological advances, the cost of producing electric power at photovoltaic power plants, allowing for both construction and operating costs, is one-tenth of what it was 20 years ago, whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased. Thus, photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants.

The conclusion of the argument is properly drawn if which one of the following is assumed?

(A) The cost of producing electric power at traditional plants has increased over the past 20 years.
(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants.
(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.
(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants.
(E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease.

Source : lsat
[Reveal] Spoiler: OA
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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15 Feb 2008, 15:14
I will go with Ans. C.

Conclusion:
Thus, photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants.

We need to support the conclusion by adding(assuming) the below ans C.
C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.

Can't wait to see OA.
Thanks,
MRD.
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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15 Feb 2008, 19:10
az780 wrote:
Photovoltaic power plants produce electricity from sunlight. As a result of astonishing recent technological advances, the cost of producing electric power at photovoltaic power plants, allowing for both construction and operating costs, is one-tenth of what it was 20 years ago, whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased. Thus, photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants.
The conclusion of the argument is properly drawn if which one of the following is assumed?

(A) The cost of producing electric power at traditional plants has increased over the past 20 years. Repetitive. This information is provided in the passage and does not help connect the arguments above.

(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants. Irrelevant. The conclusion is looking for a "less expensive" approach (or the least cost/unit). The quantity is irrelevant. So is the ratio of the various powerplants.

(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants. Correct. The second sentence states "As a result of astonishing recent technological advances, the cost of producing electric power at photovoltaic power plants allowing for both construction and operating costs, is one-tenth of what it was 20 years ago, whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased." The obvious assumption here is that the same technological advances are not applicable to traditional plants. This indirectly supports the conclusion. (To be fair, the only thing lacking in this option is a direct correlation to the conclusion)

(D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants. Irrelevant. The cost of producing electric power at photovoltaic cells is 1/10th of what it used to be. Combining this knowledge with the statement doesn't really give us anything concrete

(E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease. A good option, nevertheless incomplete. Notice the use of the word "expectation" (twice). It is unlikely that the assumption will be an expectation. IMO, it should be a fact.

It should be (C). Explanation embedded above.
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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15 Feb 2008, 23:15
D for me...

Conclusion: "Thus, photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants." we have to show that photovoltaic is less expensive than tradition plant.

premises for the conclusion: 1, cost of photovoltiac has gone down; 2, cost of traditional plant has gone up. these two premises might be fact but they are not sufficient for comparing as we don't know the starting cost levels. For instance, maybe 20 years ago photovoltiac cost 100 and now they cost 10 and traitional cost 10 and now they cost 12. From this it is clear that traditional is still cheaper. for author's conclusion to hold we have to show that the price of photovoltiac was either same or was less than the traditional plant. Choice C does that for us...
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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16 Feb 2008, 00:19
jay02 wrote:
D for me...

Conclusion: "Thus, photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants." we have to show that photovoltaic is less expensive than tradition plant.

premises for the conclusion: 1, cost of photovoltiac has gone down; 2, cost of traditional plant has gone up. these two premises might be fact but they are not sufficient for comparing as we don't know the starting cost levels. For instance, maybe 20 years ago photovoltiac cost 100 and now they cost 10 and traitional cost 10 and now they cost 12. From this it is clear that traditional is still cheaper. for author's conclusion to hold we have to show that the price of photovoltiac was either same or was less than the traditional plant. Choice C does that for us...

jay02, you have a good point. I went down that route initially, but it looks like we may not have sufficient information to quantify the statement.

Say the cost of producing electric power via photovoltaic cells 20 years back was $100. Then today, the cost is$10 (1/10 * 100). Also, say the cost of producing electric power via traditional plants, 20 years back, was $6 (possible, since 20*6 > 100). If that price has gone up to$7 today, it is still lower than the $10 it costs to produce power via photovoltaic cells. Had the numbers been a little different, it may have worked out mathematically. But for all purposes, statement D could have read "Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20000 times the cost of producing power at traditional plants." and the outcome would have been the same as the current statement. _________________ CEO Joined: 17 Nov 2007 Posts: 3589 Concentration: Entrepreneurship, Other Schools: Chicago (Booth) - Class of 2011 GMAT 1: 750 Q50 V40 Followers: 502 Kudos [?]: 3078 [0], given: 360 Re: Photovoltaic power plants produce electricity from sunlight. [#permalink] ### Show Tags 16 Feb 2008, 05:24 D due to "deny" test Very good question +1 (A) The cost of producing electric power at traditional plants has increased over the past 20 years. - paraphrasing of "whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased" (B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants. - irrelevant (C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants. - it requires "at the same cost efficiency". Maybe we can apply "the recent technological advances" but decrease costs only by 1%. (D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants. - 1/10 and 20 times give us ambiguity. But "deny" test works perfect here (E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease. - decrease by 1%? 200%?. insufficient. _________________ HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame Senior Manager Joined: 26 Jan 2008 Posts: 267 Followers: 3 Kudos [?]: 99 [0], given: 1 Re: Photovoltaic power plants produce electricity from sunlight. [#permalink] ### Show Tags 16 Feb 2008, 09:30 walker wrote: D due to "deny" test Very good question +1 (A) The cost of producing electric power at traditional plants has increased over the past 20 years. - paraphrasing of "whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased" (B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants. - irrelevant (C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants. - it requires "at the same cost efficiency". Maybe we can apply "the recent technological advances" but decrease costs only by 1%. (D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants. - 1/10 and 20 times give us ambiguity. But "deny" test works perfect here (E) The cost of producing electric power at photovoltaic plants is expected to decrease further, while the cost of producing power at traditional plants is not expected to decrease. - decrease by 1%? 200%?. insufficient. walker, whats the deny test and how does it apply to (D)? _________________ Manager Joined: 02 Jan 2008 Posts: 194 Location: Toronto Followers: 1 Kudos [?]: 35 [0], given: 0 Re: Photovoltaic power plants produce electricity from sunlight. [#permalink] ### Show Tags 16 Feb 2008, 10:17 I think its C. Reason: The stimulus suggests that photovoltic power is now cheaper because of technological advancements. Becasue of these advancements, its now cheaper to create power using photovoltic power generators. There is an inherent assumption that the technological advancments made, only apply to the photovoltic power generation and not to the traditional fossil fuel power generators. CEO Joined: 17 Nov 2007 Posts: 3589 Concentration: Entrepreneurship, Other Schools: Chicago (Booth) - Class of 2011 GMAT 1: 750 Q50 V40 Followers: 502 Kudos [?]: 3078 [1] , given: 360 Re: Photovoltaic power plants produce electricity from sunlight. [#permalink] ### Show Tags 16 Feb 2008, 10:36 1 This post received KUDOS Expert's post incognito1 wrote: walker, whats the deny test and how does it apply to (D)? (D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants. DENY (D) Twenty years ago, the cost of producing electric power at photovoltaic plants was more than 20 times the cost of producing power at traditional plants. Therefore, now the cost of producing electric power at photovoltaic plants was more than 2 times the cost of producing power at traditional plants. - it destroys the conclusion and therefore, D is necessary assumption. Actually, D also has some problems due to "the corresponding cost for traditional plants, which burn fossil fuels, has increased". But I really do not like C. _________________ HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame Senior Manager Joined: 26 Jan 2008 Posts: 267 Followers: 3 Kudos [?]: 99 [0], given: 1 Re: Photovoltaic power plants produce electricity from sunlight. [#permalink] ### Show Tags 16 Feb 2008, 11:08 walker wrote: incognito1 wrote: walker, whats the deny test and how does it apply to (D)? (D) Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20 times the cost of producing power at traditional plants. DENY (D) Twenty years ago, the cost of producing electric power at photovoltaic plants was more than 20 times the cost of producing power at traditional plants. Therefore, now the cost of producing electric power at photovoltaic plants was more than 2 times the cost of producing power at traditional plants. - it destroys the conclusion and therefore, D is necessary assumption. Actually, D also has some problems due to "the corresponding cost for traditional plants, which burn fossil fuels, has increased". But I really do not like C. Thanks for the insight. That raised a couple of questions: 1. (D) provides a valid assumption, but its "loose". The statement could have claimed that "Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 20000 times the cost of producing power at traditional plants." and that would still be applicable (kinda obvious, isn't it?) It seems I would select this if all other choices failed, as it is definitely not wrong. 2. Applying the deny test to (C) seems to have a similar outcome, but not the same: Original (C): None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants. DENY: Some of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants. IMO, both are valid options. (C) is a more "obvious" assumption straight out of the statement, and denying will alter the conclusion (though, to your point, not necessarily invalidate it). (D) is a more "inferred" assumption and clearly fails the deny test. +1 to the question poster, and for your insight. OA would be great to confirm this! _________________ CEO Joined: 17 Nov 2007 Posts: 3589 Concentration: Entrepreneurship, Other Schools: Chicago (Booth) - Class of 2011 GMAT 1: 750 Q50 V40 Followers: 502 Kudos [?]: 3078 [0], given: 360 Re: Photovoltaic power plants produce electricity from sunlight. [#permalink] ### Show Tags 16 Feb 2008, 11:16 My arguments against C: (C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants. [PP] - photovoltaic plants [TP] - traditional plants An Economic effect of the recent technological advances For example, a blade at [PP] was made from gold ($100'000) and a blade at [TP] was made from copper ($1'000). Due to inventions we can use new nanomaterial for blades and reduce cost of the blade to 950$. For [PP] economic effect is 90% but for [TP] is only 5%.
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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16 Feb 2008, 11:24
incognito1 wrote:
2. Applying the deny test to (C) seems to have a similar outcome, but not the same:
Original (C):
None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.

DENY:
Some of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants.

IMO, both are valid options. (C) is a more "obvious" assumption straight out of the statement, and denying will alter the conclusion (though, to your point, not necessarily invalidate it). (D) is a more "inferred" assumption and clearly fails the deny test.

Agree . C without information of economic efficiency is empty option...
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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16 Feb 2008, 11:51

I'm waiting
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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04 Mar 2008, 18:44
I'm going with C.

What is the OA???
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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05 Mar 2008, 09:39
I am with D on this one. Conclusion is talking about cost, C does not mention cost at all.
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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05 Mar 2008, 20:13
terp26 wrote:
I am with D on this one. Conclusion is talking about cost, C does not mention cost at all.

I am with D too!!
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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11 Jan 2009, 00:44
OA is D.

I understand what D is trying to say, but the number doesn't add up.

Lets say cost of Photovoltaic Power Plants is 19x, and cost of Fossil Fuel Plants is 1x. After 20 years, Photovoltaic Power Plants is now 1.9x and Fossil Fuel Plants increased 10% to 1.1x. Photovoltaic Power Plants is still more expensive. It doesn't go well with the conclusion that it offers a cheaper alternative.

I say they should change the number around in D a little.
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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11 Jan 2009, 03:57
billyjeans, is this the official answer?
billyjeans wrote:
OA is D.

I understand what D is trying to say, but the number doesn't add up.

Lets say cost of Photovoltaic Power Plants is 19x, and cost of Fossil Fuel Plants is 1x. After 20 years, Photovoltaic Power Plants is now 1.9x and Fossil Fuel Plants increased 10% to 1.1x. Photovoltaic Power Plants is still more expensive. It doesn't go well with the conclusion that it offers a cheaper alternative.

I say they should change the number around in D a little.
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12 Jan 2009, 09:38
ritula wrote:
billyjeans, is this the official answer?
billyjeans wrote:
OA is D.

I understand what D is trying to say, but the number doesn't add up.

Lets say cost of Photovoltaic Power Plants is 19x, and cost of Fossil Fuel Plants is 1x. After 20 years, Photovoltaic Power Plants is now 1.9x and Fossil Fuel Plants increased 10% to 1.1x. Photovoltaic Power Plants is still more expensive. It doesn't go well with the conclusion that it offers a cheaper alternative.

I say they should change the number around in D a little.

Yes, I clicked into this thread from the SC1000 software Walker wrote. Although I agree D is the better answer (the lesser of all evil), but I just don't think the number add up. I am wondering if people have any OE available. Thanks
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Re: Photovoltaic power plants produce electricity from sunlight. [#permalink]

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30 Jan 2009, 13:35
billyjeans wrote:
OA is D.

I understand what D is trying to say, but the number doesn't add up.

Lets say cost of Photovoltaic Power Plants is 19x, and cost of Fossil Fuel Plants is 1x. After 20 years, Photovoltaic Power Plants is now 1.9x and Fossil Fuel Plants increased 10% to 1.1x. Photovoltaic Power Plants is still more expensive. It doesn't go well with the conclusion that it offers a cheaper alternative.

I say they should change the number around in D a little.

Billyjeans, I agree with what you are saying and that is why exactly D should not be the answer

Negate the assumption

Twenty years ago, the cost of producing electric power at photovoltaic plants was more than 20 times the cost of producing power at traditional plants.

so 20 years ago PPP = 21x; FFP = x

now 1/10th of what it was PPP= 2.1x

whereas the corresponding cost for traditional plants, which burn fossil fuels, has increased.

FFP >x means 1.x to infinity.

So if FFP > x but less than 2.1x then the conclusion falls apart and this is a valid assumption

If FFP > 2.1x then the conclusion does not fall apart and does not need to be a valid assumption

We have both Y and N and hence we cannot say for sure.
Re: Photovoltaic power plants produce electricity from sunlight.   [#permalink] 30 Jan 2009, 13:35

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