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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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23 Apr 2009, 08:58
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Difficulty:

95% (hard)

Question Stats:

37% (02:21) correct 63% (02:33) wrong based on 601 sessions

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THIS IS A JUSTIFY QUESTION, AND NOT AN ASSUMPTION QUESTION. THESE ARE NOT ON THE GMAT

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

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

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16 May 2010, 19:13
13
1
took me 3:30, not acceptable on the GMAT. but here's why I think it's D.

12. 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. (same as conclusion, so this can't be the assumption, although true)
(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants. (we don't know anything about how much electric power here, the question is abt cost)
(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants. ( None of them can be applied is extreme and we don't know if they can be or cannot be applied, not stated in the argument)
(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.
( For this explanation I drew something like this.
...NOW......................X/10.........................................Y
...20 years ago.............X...........................................??

We don't know what the cost of producing electric power at traditional plants was 20 years ago, but we do know that........X/10 < Y......so...... X<10Y

Answer D is saying X < 20*??, assuming there is not a significant increase from ?? to Y we can say X<20Y which brings us to saying X<10Y<20Y, so definately we can say ...................
..........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. (We don't know about the future so we can't say if this is or will be true.)

Although D is not the best ans it's what is left after POE, once you start elmininating and you think a little, it pops out as a possibility, you don't have to do the mathematical stuff for it. I just did this to give some sort of a explanation.

haven't got a kudo yet, but i heard ppl asking for it, either way, let me know what you think or if there is a better explanation.

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##### General Discussion
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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23 Apr 2009, 20:07
IMO E

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 --> restating the fact
(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants -->not clearly, but it's intention is weaken
(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants --> if so, then what
(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 -->Assuming that 20 years ago, cost of producing power at traditional plants is X, so cost of producing electric power at photovoltaic plants is < 20X. So, at present, cost of producing electric power at photovoltaic plants is <2X --> make a comparison between <2X and X (increasing), can't reach any conclusion
(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 -->although it seems not too clearly, but it's the best choice. Photovalic continues to decrease, traditional remains or continues to increase, then in long-term, photovalic will be less expensive than traditional
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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23 Apr 2009, 21:30
nitya34 wrote:
12. 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.

D is the best

Nothing controls the cost of producing electric power at photovoltaic plants 20 years ago. The argument must assume something on that cost.
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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24 Apr 2009, 09:09
C

if the new technology can be applied to traditional powerplants, then traditional power plants could be just as cheap or cheaper
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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24 Apr 2009, 11:43
I was struck between C and D and took lot of time to solve this question.

C - close - talking about "use of technology" and I was considering an extra line of assumption "use of same technology = low cost"
D - - "only cost" is the concern.

IMO D.
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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29 Oct 2009, 01:29
chill wrote:
I am surprised OA is A

we must focus on what the conclusion of the argument. I am between C and D too, but only D mention about the cost whereas C mention the technology matter
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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16 May 2010, 16:20
can somebody explain better howcome it is D
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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17 May 2010, 02:49
you need to get kudos for this firang nice & intelligent explanation.
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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17 May 2010, 08:41
Thanks raghav for my first kudo
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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12 Jun 2018, 03:13
I think this is a very good question because the correct answer states an assumption that doesn't make the conclusion always true but still is required.

For the conclusion that a price reduction of photovoltaic electricity led to a lower price than that of tradtionally produced electricity to be true, it is necessary that the price of the photovoltaic energy was less than 20 times the price of tradtionally produces energy. We could also state a similar assumption that the prices was less than 50 times that of tradtionally produces energy. This assumption is definitely required.
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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30 Jun 2018, 14:49
Shouldn't the correct OA read : Twenty years ago, the cost of producing electric power at photovoltaic plants was less than 10 times the cost of traditional power,?
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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17 Jul 2018, 12:18
Negating Option D :
Twenty years ago, the cost of producing electric power at photovoltaic plants was at least 10 times the cost of traditional power.

Now consider,

Cost of Photo Plant 20 years ago = P
Cost of Traditional Plant 10 years ago = T
Now, P >= 20 T
Suppose P= 25T
Present Photo Plant Cost = P/10 =2.5T
Since Traditional Plant cost also increased , but stimulus doesnt mention the increase , let us suppose that T at present is 100T
2.5Tis not less than 100T . This doesnot break down the conclusion

Assumption negation test failed .
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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18 Jul 2018, 08:24
Minheequang wrote:
IMO E

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 --> restating the fact
(B) Twenty years ago, traditional power plants were producing 10 times more electric power than were photovoltaic plants -->not clearly, but it's intention is weaken
(C) None of the recent technological advances in producing electric power at photovoltaic plants can be applied to producing power at traditional plants --> if so, then what
(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 -->Assuming that 20 years ago, cost of producing power at traditional plants is X, so cost of producing electric power at photovoltaic plants is < 20X. So, at present, cost of producing electric power at photovoltaic plants is <2X --> make a comparison between <2X and X (increasing), can't reach any conclusion
(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 -->although it seems not too clearly, but it's the best choice. Photovalic continues to decrease, traditional remains or continues to increase, then in long-term, photovalic will be less expensive than traditional

What do you think?
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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18 Jul 2018, 12:01
This is a JUSTIFY question and not an assumption question. These are questions that are almost identical to assumption questions, but are testing a different aspect of your skills. Hence why the negation technique is not the way to go about this question. If you are not taking the LSAT, please stay away from this question as it will only confuse you.

Here is an explanation from Powerscore: https://forum.powerscore.com/lsat/viewtopic.php?t=9113
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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18 Jul 2018, 18:28
This is a JUSTIFY question and not an assumption question. These are questions that are almost identical to assumption questions, but are testing a different aspect of your skills. Hence why the negation technique is not the way to go about this question. If you are not taking the LSAT, please stay away from this question as it will only confuse you.

Here is an explanation from Powerscore: https://forum.powerscore.com/lsat/viewtopic.php?t=9113

nightblade354 Useful contribution but I still have following in the explanation provided. I posting the explanation here for continuity in the forum discussion.

On a number of occasions the correct answer to a Justify question has been something that is also an Assumption of the argument (and vice versa). The difference is that Justify answers can also contain elements that are not necessary to the argument. It just depends on what the test makers decide to do.

Turning to the problem at hand, this is one that I've always liked, primarily because I feel as though it's a great example of how topic can influence our analysis. Most students, when they see "photovoltaic power plants," kind of go into a fugue state and just disconnect from the problem. I used to joke in class that if this question was about cheeseburgers or diamonds (things that people are familiar with), everyone would get it right. Let's analogize it and see:

Kobe beef has traditionally been one of the most expensive forms of protein in the world. As a result of advancements in farming and production, Kobe beef now costs 1/10 of what it did 20 years ago. Traditional cheeseburgers, on the other hand, have become slightly more expensive. Thus, Kobe beef is now a cheaper way to get protein than a traditional cheeseburger.

Or, let's say it was about diamonds:

Diamonds have traditionally been one of the most expensive gems in the world. As a result of advancements in production, diamonds now costs 1/10 of what they did 20 years ago. Cubic zirconia, a synthetic form of diamond, on the other hand, have become slightly more expensive. Thus, diamonds are now cheaper than cubic zirconia.

These two examples may make the problem clearer: even though the expensive item has dropped in price, that doesn't now mean it is less expensive than the originally cheaper alternative. If a diamond used to cost \$1000 and a cubic zirconia cost \$10, even when the diamond is 1/10 the price (\$100), it is still more expensive than the cubic zirconia.

In this light, answer choice (D) suddenly makes a lot more sense, because it addresses the initial price difference, and shows that when you drop the price to 1/10, it would be lower than the other item.

This last statement does not agree with numbers mentioned above in the explanation.

i.e. explanation does not make choice D) clear winner.......

Will like to have your take on this....
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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19 Jul 2018, 05:04
Harshgmat,

That is the point. Justify questions are more like strengthen/weaken questions. We just want to fill the missing piece of information. In this example, the missing information was original cost. We do not care about future cost because the question is exclusively about the present. Is it a perfect question? Nope, as your math shows. But (D) is the best answer given the circumstances.
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Re: Photovoltaic power plants produce electricity from sunlight.  [#permalink]

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19 Jul 2018, 09:12
Harshgmat,

That is the point. Justify questions are more like strengthen/weaken questions. We just want to fill the missing piece of information. In this example, the missing information was original cost. We do not care about future cost because the question is exclusively about the present. Is it a perfect question? Nope, as your math shows. But (D) is the best answer given the circumstances.

Still I am finding it what I will say a bitter pill...

I will need some more time with such type of questions...

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

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29 Dec 2018, 23:27

As the argument is stated, there is a logical gap between the information given in the premises and the claim made in the conclusion:

Premise 1: The cost of producing electric power at photovoltaic power plants is one-tenth of what it was 20 years ago.

Premise 2: The corresponding cost for traditional plants has increased.

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

From the fact that one cost has gone down while another has risen, it does not necessarily follow that the first is now lower than the second. In particular, if the cost of producing electric power at photovoltaic power plants twenty years ago was more than ten times the corresponding cost for traditional plants, then the fact that it is now one-tenth what it was is not sufficient to show that it is now lower than the corresponding cost for traditional plants, even though we are told in Premise 2 that the cost for traditional plants has increased. To conclude from the premises given in the argument that photovoltaic power plants now offer a less expensive approach than do traditional power plants, we need to know how the costs of the two methods of production were related 20 years ago—specifically that the cost of producing power at photovoltaic plants was less than 10 times the cost of producing it at traditional plants. (D) gives this information and is, thus, the credited response.

Response (A) is incorrect because it tells us about only one of the two costs, not about how the two were related 20 years ago. It in effect restates premise 2, and premises 1 and 2 together are not sufficient for drawing the conclusion.

Response (B) is incorrect. The amount of electricity produced by the different kinds of plants is not at issue.

Response (C) is incorrect. While it is relevant to the discussion, (C) does not provide the information about the comparative costs of the two kinds of plants 20 years ago that allows the conclusion to be properly drawn.

Response (E) is incorrect because the conclusion in the argument is about the present only. Whether or not the change described in (E) is expected to take place has no bearing on the claim in the conclusion that the one kind of plant offers a less expensive approach at present.

OPTION: D
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Re: Photovoltaic power plants produce electricity from sunlight.   [#permalink] 29 Dec 2018, 23:27
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