Last year all refuse collected by Shelbyville city services was incine

I'll go with (D)

Examining the stem:

Last year:
All refuse (collected in N truckloads) --- incinerated ---> residue ash

This year:
All refuse --- separate for recycling ---> refuse to be incinerated (resulting in half the previous year's truckloads N/2) ---- incinerate this left over refuse ----> residue ash (which is half the last year's quantity)

Therefore, this year only half the amount of residue is being incinerated. So, unless each truckload generates less residue ash than it did last year, the objective cannot be achieved.

Responding to a pm:

Argument:

Last year all refuse was incinerated.
This generated a large quantity of residual ash.
Plan: Separate for recycling refuse to reduce the number of truckloads of refuse to be incinerated to half of last year's number.
Aim of the Plan: to reduce the amount of residual ash Shelbyville generates this year to half of last year's total.

The plan is to reduce the refuse to half of last year's.

If last year 100 truckloads were incinerated, this year only 50 should be incinerated. So even if we collect 150 truckloads this year, 100 should be separated to recycle and only 50 should be incinerated. Then the residual ash will be half of last year's.

There are some requirements for the plan to work:

- There should be at least this much recyclable stuff in the refuse collected. We must have at least 100 truckloads of recyclable stuff so that we are left with 50 truckloads to incinerate.

- Half the number of truckloads should produce half the residual ash. What if the residual ash amount depends on the kind of refuse? If certain refuse produces more ash and if that is the kind of refuse we have in 50 truckloads this year, it will produce more than half of last year's ash.

Look at the options now:

(A) This year, no materials that city services could separate for recycling will be incinerated.

This is not required. If all 150 truckloads are recyclable, we could incinerate 50 truckloads and our plan could work. It is not necessary to separate all recyclable stuff.

(B) Separating recyclable materials from materials to be incinerated will cost Shelbyville less than half what it cost last year to dispose of the residual ash.

Cost is irrelevant to the argument.

(C) Refuse collected by city services will contain a larger proportion of recyclable materials this year than it did last year.

Incorrect. The proportion of recyclable material compared with last year's proportion is immaterial. We don't have any data about the last year's proportion. Perhaps last year all refuse was recyclable. Then we don't need and cannot have a larger proportion. What we need is a large enough proportion of recyclable material but we don't necessarily NEED MORE THAN last year's proportion. This option is incorrect because of the comparison it makes.

(D) The refuse incinerated this year will generate no more residual ash per truckload incinerated than did the refuse incinerated last year.

This is one of our requirements. The second one. Hence this is correct.

(E) The total quantity of refuse collected by Shelbyville city service's this year will be no greater than that collected last year.

This is not necessary. In our example, we assumed that this year 150 truckloads was produced against 100 truckloads of last year.

Answer (D)

There's no doubt about it...Assumptions questions are one of the toughest question types in CR.

At a 700 level, you will not have the time to analyse every option in detail. So it is a good idea to train hyourself to look out for typical patterns in the information presented in the argument.

Let's try to break down the information presented.

Simply put...

The argument says that Shelbyville needs to cut the amount of residual ash generated by half.



To do this the city has to cut the number of truckloads of garbage being burnt by half.



Very logically, the city is obviously assuming that...



Keeping this simple logic in mind, let's look at the options...

A. This year, no materials that city services could separate for recycling will be incinerated.

We know this already. “Recycling” implies that something will be used again in some form. Even if we negate this option: “Materials that could have been separated for recycling will be incinerated” – notice that all you have to do is remove the “no” – it does not affect the conclusion that if the number of truckloads to be incinerated is cut down to half of last year's total then the amount of ash generated will also come down by half. Eliminate!

B. Separating recyclable materials from materials to be incinerated will cost Shelbyville less than half what it cost last year to dispose of the residual ash.

We do not need to assume anything about how much the process of garbage separation will cost. Eliminate!

C. Refuse collected by city services will contain a larger proportion of recyclable materials this year than it did last year.

How much refuse is collected or what proportion of that refuse is recyclable is irrelevant. What has been concluded is that if the number of truckloads of garbage burned is cut down to half of last year’s total, then the amount of ash generated will also come down by half. This can be concluded whether this year's refuse contains a larger proportion of recyclable materials or not. Eliminate!

D. The refuse incinerated this year will generate no more residual ash per truckload incinerated than did the refuse incinerated last year.

Let’s quantify this. Let’s imagine that 20 truckloads of garbage were burned, and this generated 100 pounds of residual ash. The author has concluded that if half the amount, i.e., 10 truckloads of garbage is burned, only 50 pounds of residual ash will be generated. If this is so, then the author has clearly assumed that the rate at which ash will be generated will be the same this year also. If we negate: “The refuse incinerated this year will generate more residual ash per truckload incinerated than did the refuse incinerated last year”. If the rate of generation of residual ash is greater than the conclusion falls. Select!

E. The total quantity of refuse collected by Shelbyville city service's this year will be no greater than that collected last year.

The amount of refuse that has been collected is not relevant. Eliminate!

- Nitha Jay
GMAT Verbal SME

Okay, let's take this baby down. We are going to focus on the strategies behind this question that will help you answer this and many other GMAT problems. As with all Critical Reasoning questions, the first thing we need to do is a little research in the question stem. It asks us for something that would be required for the collection program to achieve its aim. Such phraseology tells us this is a “Plan/Strategy” question, a variation on the traditional “Strengthen” question type. This defines our strategy. With Plan/Strategy questions, we aren’t necessarily looking for a conclusion to strengthen, but we are looking for goals. Often, the logical gap we are looking for is between the elements of the plan and what the plan actually wants to accomplish.

According to the stimulus, the goal is to “reduce the amount of residual ash this year to half of last year’s total.” The plan is to separate recycling so that there are half the number of truckloads to be incinerated. Does half of the truckloads necessarily lead to half the ash? Not necessarily. Therein lies the logical gap. We need to show that the reduction of truckloads will lead to the commensurate reduction in ash. If not, the plan’s goals won’t be met.

The correct answer to this question is “D”. However, we are going to skip “D” for a little bit to look at the wrong answers. For those of you studying for the GMAT, it is just as important to know why an answer choice is WRONG as it is to know why an answer choice is correct. Let’s watch what the GMAT does here to test your critical-thinking skills.


Answer choice “A” doesn’t address the logical gap. Pay attention to what the question is asking: we are looking for a fact "required" by the argument to function. That is a pretty high bar. Is it necessary that "no materials" be incinerated if they could be recycled? No. The city could incinerate recyclable materials and still keep the truckload limit down to half of the total. While "A" adds the fact that the separated materials won’t be incinerated, it still tells us nothing about the amount of ash generated per truckload. "A" isn't required by the argument, and it doesn't tell us why half the truckloads leads to half the ash. If you picked answer choice "A", your brain inserted a lot of unjustifiable assumptions into the argument (such as recyclable materials supposedly generate the same amount of ash as non-recyclable materials.) But we don't know this. What if the recyclable materials take up large amounts of space in a truckload, but leave little ash? Answer choice “A” is not it.


Answer choice “B” is an example of a beautiful trap by the GMAT I call a “Distracting Detour.” Distracting Detours happen when the GMAT intentionally swaps out the initial goals or conclusion in a question for a different (possibly compelling) set of goals, tricking you into thinking that these alternate goals matter. However, the change doesn’t answer the question, plug the logical hole, or meet the goal. In the case of this question, the goal is to reduce ash, not reduce cost. Thus, cost is irrelevant. Answer choice “B” falls by the wayside.


Answer choice “C” also doesn’t focus on the logical gap. The stimulus states that the program will remove “recycling ENOUGH” to reduce the number of truckloads. Even if answer choice “C” were false, it would still be possible to say that we removed “ENOUGH” recycling for the logic to work. This is especially true since we don’t know relative amounts of recycling from last year to this year to even know if it would matter that the amount of recycling is increasing. Maybe it doesn’t matter. Answer choice “C” is out.


Answer choice “E” is very similar in nature to answer choice “C”. The plan is to remove “recycling ENOUGH” recycling that the number of truckloads to be incinerated is half of last year’s number. Thus, even if answer choice “E” were false, it would still be possible to remove “recycling ENOUGH” recycling. It could still be possible to have the total amount of refuse go up and still remove “recycling ENOUGH” recycling. We don’t need answer choice “E” for the plan to still function. Get rid of “E”.


However, answer choice “D” is critical and focuses on the necessary logical gap. Remember, our gap is: “Does half of the truckloads necessarily lead to half the ash?” Answer choice “D” talks about the ash per truckload. If each truckload generated more ash, then we wouldn’t see a commensurate reduction in ash. By saying that each truckload doesn’t generate more ash than previous years, if we can reduce the amount of truckloads by half, we are reducing the amount of ash by at least one half. Answer choice “D” is it.

Now, let’s look back at this problem from the perspective of strategy. This problem can teach us several patterns seen throughout the GMAT. First, when a question asks you for additional information that is "required" for an argument to work, focus EXACTLY on what the problem is asking. Many people miss Critical Reasoning questions because they rush too quickly through the interpretation of the question and miss crucial leverage words. Remember that "required" information has a pretty high standard: you must look for information that is crucial for an argument to even function, not just for information that makes the argument sound better. Focusing on the exact logical gap keeps us from falling for distracting traps and detours. And that is how you think like the GMAT.

Dear Friends,

Here is the detailed explanation to this question-




Mind-map: Halve the number of truckloads for incineration → Halve residual ash.

Missing link: Between halving truckloads to be incinerated and halving residual ash.

Expectation from the correct answer choice: To provide link between halved truckloads for incineration and halving of residual ash.

Choice A: This answer choice only remarks that the recyclable refuse shall not be incinerated; it does not provide sufficient grounds to conclude that this measure will ensure that the amount of residual ash will be halved in consonance with the halving of collected truckloads for incineration. Furthermore, since the number of truckloads destined for incineration are going to be halved regardless of whether or not any recyclable refuse shall be included therein, this answer choice does not provide a link between halved truckloads for incineration and the halving of residual ash; therefore, it is an incorrect answer choice.
Choice B: This answer choice remarks on the decrease in residual ash disposal costs due to recycling and does not touch upon the reduction of residual ash amounts in the slightest; while recycling efforts will certainly reduce the amount of refuse destined for incineration and save on incineration costs thereby, this does not signify a halving of the amount of residual ash; as it does not provide a link between halved truckloads for incineration and the halving of residual ash, it is an incorrect answer choice.
Choice C: This answer choice is irrelevant as we are not concerned with how much refuse is collected or how much of it is recyclable; already, the number of truckloads destined for incineration are to be halved, and this will happen irrespective of the proportion of recyclable materials. Furthermore, if the proportion of recyclable material is high, the incinerated material will be lesser; however, that does not essentially mean that the ash per unit of refuse will also be reduced; as this answer choice does not provide a link between halved truckloads for incineration and halving of residual ash, it is an incorrect answer choice.
Choice D: This answer choice provides a necessary condition for the desired halving of residual ash, alongside the given information that the number of truckloads collected will also be halved; if the number of truckloads to be incinerated will be halved, and the amount of residual ash for each truckload after incineration will be no more than it was the previous year, it follows logically that the amount of residual ash produced this year will be no more than half of last year’s; as this answer choice links the halving of truckloads to the halving of residual ash, it is the correct answer choice.
Choice E: This answer choice is irrelevant, as it states that the amount of refuse collected this year will remain the same as last year, which does not matter, as the number of truckloads to be incinerated will be halved regardless; it does not affect the final amount of refuse to be incinerated and, consequently, the amount of residual ash in the slightest; therefore, it does not address the link between halved truckloads for incineration and the halving of residual ash, and is an incorrect answer choice.

Hence, D is the best answer choice.

To understand the concept of “Characteristics of an Evaluation Statement,” you may want to watch the following video (~3 minutes):



All the best!
Experts' Global Team

Will for D as well. I debated with myself whether A was right. However I discounted A because I reasoned that we don't have any info on how much ash the recyclable materials would produce. Also, I think the very reason why the recyclable materials are being separated because they are NOT to be incinerated. So there's no reason to assume they would be.

Can somebody enlighten me if this reasoning for eliminating A sounds ok?

Thanks

Hi ratinarace,

First, lets determine the question type. The answer choice has to be true for the conclusion to be true i.e. it is an assumption question.

Conclusion is that Shelbyville city service will achieve its aim.

In simple words the stimulus says that last year the incinerator produced a lot of residual ash. This year they want to reduce the residual ash by cutting to half the the refuse sent to the incinerator.

In more simpler words the author is assuming: reduction in refuse to half = reduction in residual ash to half .

If an answer choice states this assumption, we've got the answer. Even if you have not got this assumption initially you can run through the answer choices and check which one would make the conclusion/ aim true for sure.

(C) Refuse collected by city services will contain a larger proportion of recyclable materials this year than it did last year.


Does this has to be true for the conclusion to be true. If recyclable material is high then the incinerated material will be low, but it could still generate more ash per unit of refuse. So, it is not mandatory for (C) to be true for conclusion to be true.

(D) The refuse incinerated this year will generate no more residual ash per truckload incinerated than did the refuse incinerated last year.

Does this has to be true for the conclusion to be true. Yes, lets see why;

the amount of ash per unit refuse is less than or equal to the amount of as per unit last year. Therefore, the incinerator would generate less than or equal to the amount of residual ash produced last year. This has to be true for the conclusion to be true. So, it is our answer.

(E) The total quantity of refuse collected by Shelbyville city service's this year will be no greater than that collected last year.


This need not be true for the conclusion to be true. The quantity of refuse could be the same or greater but the proportion of waste that is incinerated be less than what it was last year. The Shelbyville city service could still achieve its aim without (E) being true.

Hope that helps,

Vercules

Lets see what choice E states:



The total quantity of ash collected is immaterial. Why!! because of the last line of the argument:



It can be inferred from the above line that regardless of the amount of refuse collected, the city services will only send half the truckloads. Hence, the amount of refuse collected does not matter. Even if 10X the refuse is collected this year, still the # of truckloads sent for incineration will be half of last year's number.

- Rajat Sadana

I'm still confused as to why the answer is not A. If any of the recycled products are incinerated, then this affects the total amount of residual ash which counteracts the intention of halving the amount of refuse to be incinerated does it not?

Your reasoning that, if any of the products separated for recycling are somehow incinerated rather than recycled, the city won't achieve its goal makes sense. However, (A) is not about products separated for recycling. (A)is about products that COULD BE separated but are not.

The passage says, "This year city services will separate for recycling enough refuse to reduce the number of truckloads of refuse to be incinerated to half of last year's number."

In the process of separating "enough refuse to reduce the number of truckloads ... to half of last year's number" the city may not separate all materials that could have been recycled, and so, some materials that could have been separated for recycling may be incinerated. All the same, as long as the city separates enough to reduce the number of truckloads by half, the city can meet its goal.

So, the success of the plan does not depend on what (A) says.

In Critical Reasoning, any word or detail can make a difference. In this case, the key detail that you have to notice in order to eliminate (A) is that (A) is not about material that has been separated but rather about material that "could" be separated.

Hi GMATNinja,

Thank you for your explanation.

However, I have some doubt on A.

If A is not true, some material that COULD have been separated for recycling gets incinerated.

Doesn't it mean that there will be at least more ash, more than half of the amount of the last year because incinerating some
recycling material can generate ash. Even though we assume D to be true, if A is not true , the conclusion that "to reduce the amount of residual ash Shelbyville generates this year to half of last year's total" can be weakened.

Please explain.
Thank you.

Let's just pretend that Shelbyville separates ALL of the materials that COULD be separated for recycling. And let's pretend that, if they do that, number of truckloads of refuse to be incinerated will be reduced by 75%.

But Shelbyville's goal is only to reduce the number of truckloads to HALF of last year's number. If they separate ALL possible materials for recycling, they might EXCEED their goal. That would mean that they'd have some wiggle room: even if some of those recyclable materials get incinerated, they could still meet their goal.

That's why (A) is not REQUIRED for the revamped collection program to achieve its aim: Shelbyville could meet its goal even if, for example, they only separate some/most of the material that could be separated for recycling.

I hope that helps!

Passage Analysis

• Last year all refuse collected by Shelbyville city services was incinerated.

o All the waste collected by the city services in Shelbyville last year was disposed by incineration.

• This incineration generated a large quantity of residual ash.

o This burning to dispose the garbage lead to the production of massive amounts of ash residue.

• In order to reduce the amount of residual ash Shelbyville generates this year to half of last year's total, the city has revamped its collection program.

o Shelbyville city services intend to decrease the total quantity of residual ash to be generated this year to half of the quantity generated last year.
o For this purpose, the city has renovated its garbage collection program.

• This year city services will separate for recycling enough refuse to reduce the number of truckloads of refuse to be incinerated to half of last year's number.

o This year, the city services will segregate the waste and recycle a part of it.
o The plan is to re-channel a part of waste from the trash truckloads to be recycled.
o Enough refuse will be sent to be recycled so that the number of truckloads of waste left to be incinerated will be half of the corresponding number in the previous year.

Conclusion: This year, Shelbyville city services’ revamped collection program will reduce the amount of residual ash Shelbyville generates this year, to half of last year's total.

Question Stem Analysis
We are required to find out the necessary assumption if the program should achieve its aim.

Pre-thinking

Falsification Question
In what scenario is it possible that Shelbyville city services’ revamped collection program will not reduce the amount of residual ash generated this year, to half of last year's total?
Given that
• Last year all refuse collected by Shelbyville city services was incinerated.
• This incineration generated a large quantity of residual ash.
• In order to reduce the amount of residual ash Shelbyville generates this year to half of last year's total, the city has revamped its collection program.
Thought Process
The goal of the revamped collection program is to halve the quantity of residual ash generated by incineration of garbage, as compared to last year. For this, the city services plan to separate enough of the waste to be recycled and incinerate only the amount of waste equivalent to half the number of truckloads of refuse incinerated last year. Here we can see that there is an underlying assumption connecting the truckloads of waste incinerated and the amount of residual ash produced.

Falsification Condition
What if a truckload of trash produced this year will generate more residual ash on incineration than the ash from the same amount of trash incinerated last year? In that case the program will not achieve its aim even if the premises hold true.
Assumption
A truckload of trash produced this year will generate no more residual ash on incineration than what is generated from the same amount of trash incinerated last year.

Answer Choice Analysis

(A) This year, no materials that city services could separate for recycling will be incinerated.
INCORRECT
This information is unnecessary and does not go with the passage. The author explains that only an amount of refuse will be removed from the loads for incineration such that what is left will produce only half of the total residual ash produced last year. It does not matter whether anything more is suitable for recycling. Hence this is a wrong choice.

(B) Separating recyclable materials from materials to be incinerated will cost Shelbyville less than half what it cost last year to dispose of the residual ash.
INCORRECT
The only goal of the city services is to reduce the amount of residual ash produced to half the previous year’s quantity. Price is not a concern for the plan. Hence, it is an incorrect choice.

(C) Refuse collected by city services will contain a larger proportion of recyclable materials this year than it did last year.
INCORRECT
This information is unnecessary and irrelevant, as last year, no recycling was done at all. Hence, this is not a correct choice.

(D) The refuse incinerated this year will generate no more residual ash per truckload incinerated than did the refuse incinerated last year.
CORRECT
This statement is in line with our pre-thought assumption 1 and hence the correct answer choice.

(E) The total quantity of refuse collected by Shelbyville city service's this year will be no greater than that collected last year.
INCORRECT
This information is also unnecessary in this context, as even if the total quantity of refuse is greater, it need not affect the success of the program, as a significantly higher quantity of waste could be recycled to achieve the program’s aim. Hence, this choice is also an incorrect option.

This year city services will separate for recycling enough refuse to reduce the number of truckloads of refuse to be incinerated to half of last year's number.

i have a serious problem here! Can anyone help? I don't understand what the question is saying!.

Wil separate (verb here imo), where is the object? Separate for recycling enough refuse? What does this mean????

The sentence in the passage is:

From this, we know that:

• This year -- whatever is happening is occurring this year
• city services -- this is the subject of this sentence, these are the people doing the action
• will separate -- this is what the city services will do
• for recycling -- this is what will happen to whatever is separated
• enough refuse -- BINGO!! Here is the object. The refuse (or trash) is what is being separated and enough tells us the amount that will be separated
• to reduce the... -- this is why the refuse is being separated. The goal is to reduce the number of truckloads of refuse incinerated by half, compared to last year's number.

So this sentence could be rewritten to say:

City services will separate refuse for recycling this year. They want to reduce the number of truckloads of refuse to be incinerated this year to half the number that was incinerated last year. So, they will separate enough refuse to achieve that goal.

I hope that helps!

If one of the option is :

No material that is separated for recycling could be incinerated.

Can this be right answer?
If any more recycle material could be incinerated then it would add more ash and it could weaken the argument

OR

We are only concerned about materials that have been taken by trucks , numbers of which have been reduced to half.
What is incinerated as left out ( no carried by trucks) does not matter?

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