#12 - Photovoltaic power plants produce electricity from sun

[Administrator]

Complete Question Explanation

Justify the Conclusion-#%. The correct answer choice is (D)

The stimulus concludes that photovoltaic power plants offer a cheaper way of meeting energy demands than do traditional power plants. That is supported by the observation that the cost of building photovoltaic plants and producing electricity at those plants is 10% of what it had been 20 years ago, and the cost of traditional plants and production has increased.

The argument is not significantly flawed with respect to ignoring part of the cost equation, because it clearly discusses both building and energy production. The major flaw in the argument is that it ignores the possibility that 20 years ago the total cost of photovoltaic power production was so extremely high that even 10% of that cost might still be too much. Since you are asked to justify the argument, you need to address that major flaw.

Answer choice (A): This does not justify the argument. The major problem was that photovoltaic plants might still create more cost, and you need to address that. This response does not. Furthermore, it is questionable that this response even contains new information, since "operating" costs could include "production" costs.

Answer choice (B): The fact that traditional plants supply more of the available power output is not relevant to whether one type of plant is more cost-effective, so this choice is wrong.

Answer choice (C): If the technological advances could be applied at traditional plants, that would challenge the argument, so this response does strengthen the argument by eliminating that possibility. However, even given this new information, the traditional plants could be less expensive, so this response does not justify the conclusion. Though attractive, this response is incorrect.

Answer choice (D): This is the correct answer choice. If the of photovoltaic power was less than 10 times the cost of traditional power, and photovoltaic costs have reduced to 10 percent of that figure, while traditional costs have increased, photovoltaic power does currently cost less. You can consider these numbers:

• 20 years ago: Photovoltaic cost: $100. Traditional cost: $11.
  
  Now: Photovoltaic cost: $10. Traditional cost: $12.

Answer choice (E): Since the argument is about what is currently the case, what happens in the future does not prove that photovoltaic power is currently the more cost-effective. Furthermore, the fact that photovoltaic costs decrease does not prove that they will ever fall to the level of traditional power.

[Arindom]

Hi,

So, the author's conclusion is that photovolatic power plants offer a less expensive approach to meeting demand for electricity than traditional power plants. The premises are - the cost of producing electric power at photovoltaic plants is 1/10th of what it was 20 years ago but this is not the case with traditional plants where the corresponding has increased.

I picked ans choice C. I kind of approached it as an Assumption question. Could you explain why answer choice C is incorrect and D is correct? Is it possible to diagram this?

Also, generally for Justify questions, would an answer choice that is necessary to the argument also work?

Thanks.

- Arindom

[Dave Killoran]

Hi Arindom,

Thanks for the questions! In answer to your Justify/Necessary question, the answer is yes. 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.

With answer choice (C), the problem is that knowing the technological advances cannot be applied still doesn't prove the conclusion because of the bigger issue: the relative starting costs. If we knew those, then (C) might come into play, but we'd more information even at that point.

Last, because this is numbers and percentages, I wouldn't diagram it.

Please let me know if that helps. Thanks!

[Arindom]

Thanks, Dave! Really clear!

- Arindom

[biskam]

Hi Arindom,

Thanks for the questions! In answer to your Justify/Necessary question, the answer is yes. 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.

With answer choice (C), the problem is that knowing the technological advances cannot be applied still doesn't prove the conclusion because of the bigger issue: the relative starting costs. If we knew those, then (C) might come into play, but we'd more information even at that point.

Last, because this is numbers and percentages, I wouldn't diagram it.

Please let me know if that helps. Thanks!

so what the examples (the ones provided by Dave and the one in the stimulus) show is that the only way we can prove the conclusion to be true is if the alternative (here, the photovoltaic power, the kobe beef, the diamonds) was originally cheaper than the traditional choice (the traditional power, the cheeseburger, the cubic z). If this is true, then no matter the decrease in the alternative or the increase in the traditional, the alternative is always going to be cheaper than the traditional because there's a gap... am I getting this right?

Constantly havign struggles with #% questions

[nicholaspavic]

the only way we can prove the conclusion to be true is if the alternative (here, the photovoltaic power, the kobe beef, the diamonds) was originally cheaper than the traditional choice

Yes biskam, you are definitely getting the idea, but I will add one other point. It is not the only way. What if the alternative and the traditional had the same price originally? Then in that case the decrease of the alternative and the slight increase in the traditional would then also translate into a situation where it could be justified. But you are definitely getting stronger at the #%'s questions, so well done!

Thanks for the great question.

[whardy21]

I was down to E, C and D on this question and chose E. I agree with the explanation as to why E is wrong. However, if we are trying to add a choice that proves about what happens currently, how does answer choice D fit that mold. My question is, just as the problem with E, why should we care about Twenty years ago about the cost of producing electric power? If we are looking for an answer choice that can currently prove the conclusion is valid, how is D the correct answer? Please help. Thanks.

[Adam Tyson]

It's basically a math problem, whardy21. The author wants to prove the conclusion that "photovoltaic power plants offer a less expensive approach to meeting demand for electricity than do traditional power plants." In other words, the cost per unit of energy at a photovoltaic plant today is less than the cost of that same unit of energy at a traditional, fossil-fuel plant today.

What's his evidence? Photovoltaic got cheaper by a factor of 10 over the past 20 years, while traditional got more expensive over the same timeframe. Does that prove that today the former is cheaper than the latter? Not without knowing more. We need to know what the costs were when we started in order to prove that mathematical conclusion.

We used an example earlier in this thread, and it's worth looking over to see why we care about what the prices were 20 years ago. Here's another example:

In the past decade, my annual income has gone up, while my brother's annual income has gone down. Therefore, I now make more money than my brother.

How do I prove that conclusion? I need some numerical information to do it. If he and I made the same income 10 years ago, or if I made more than he did even then, then given my premises I must be making more than he is now. But what if that's not true? What if he made more than me back then? Couldn't he still be making more than me now, despite his decrease and my increase? Maybe he went from making a cool million a year down to a paltry $750k, while my unemployment income of about $15k a year rose to $25k. (That reminds me, I need to ask my brother to loan me some money again).

Answer C has nothing to do with the numbers here, and proves nothing about the relative costs of the two types of energy production. Answer E is about the future, and proves nothing about where we are right now. Only answer D provides the info we need - if we know where we started from (answer D), and we know what has changed (the premises), then we know where we are right now (the conclusion). Knowing the change without knowing the starting point, or knowing the starting point without knowing the change, will get us nowhere, which is where we were with the stimulus and without answer D.

Play with the numbers on your own and you'll see why D does the job!

[ahorita]

So, I've already gone through equations on other replies.

Let's say Ppp was $100 20 years ago, and now $10
while tpp was $8 20 years ago, and now $11(as it doesn't say how much it had increased)

20 yrs ago, tpp was way cheaper than Ppp and it was more than10 times of tpp.
Still, currently Ppps offer a less expensive approach than tpp.

So my question would be, not knowing the increase rate of TPP, why do we have to assume that TPP*10 > Ppp 20 years ago?

[Rachael Wilkenfeld]

Hi Ahorita,

We aren't assuming it, but we are going based on what the stimulus says. For justify the conclusion questions, we want to think to ourselves about what the stimulus is lacking. What's missing? Where's the jump in the argument between the premises and the conclusion? We aren't assuming any information, but we are thinking about what information is missing that could either prove the conclusion, or that has to be eliminated in order to prove the conclusion.

In this case, the stimulus doesn't give us enough information to rule out the possibility that the traditional plants are still less expensive than the photovoltaic plants. That's a flaw in that argument, and we need to address it in order to justify the conclusion. The conclusion here is that photovoltaic plants are less expensive, so we need to rule out the possibility that they are more expensive. That's what answer choice (D) does for us. Adding that information to the stimulus, we would be able to justify the conclusion that photovoltaic plants are less expensive.

Hope that helps!
Rachael