Leachate is a solution, frequently highly contaminated, that develops

Question

Leachate is a solution, frequently highly contaminated, that develops when water permeates a landfill site. If and only if the landfill’s capacity to hold liquids is exceeded does the leachate escape into the environment, generally in unpredictable quantities. A method must be found for disposing of leachate. Most landfill leachate is send directly to sewage treatment plants, but not all sewage plants are capable of handling the highly contaminated water.

Which one of the following can be inferred from the passage?

(A) The ability to predict the volume of escaping landfill leachate would help solve the disposal problem.

(B) If any water permeates a landfill, leachate will escape into the environment.

(C) No sewage treatment plants are capable of handling leachate.

(D) Some landfill leachate is send to sewage treatment plants that are incapable of handling it.

(E) If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.

beckee529 · Accepted Answer

I was stuck between D and E but I think E is stronger.

(D) Some landfill leachate is send to sewage treatment plants that are incapable of handling it.  even though there are plants that are incapable of handling leachate (as it was mentioned in the last sentence), it would be presumptuous of us to assume that the leachate are actually sent to those plants. Maybe leachates are only sent to sewage plants that can handle it. We cannot say. 

(E) If leachate does not escape from a landfill into the environment, then the landfill's capacity to hold liquids has not been exceeded.  as stated in the argument - "if and only if".

Testluv · Answer

Hi,

an inference is an implied conclusion. But on a GMAT inference question, if you see an answer choice that must be true based on the stimulus, you should always automaticlaly select it. There are two reasons for this: a) what you think is a simple paraphrase may actually have something new in it, and can thus be regarded as a proper inference; and b) some questions simply ask you to treat the passage as true, and select a choice that "must be true"--in these cases, the correct answer may even be a restatement of one of the statements in the passage.

In a GMAT inference question, a choice that must be true based on one or more statements in the passage is ALWAYS automatically correct.

Thus, the the four wrong answers are things that could be false.

Let's apply this approach to this question.

In the passage we learn that leachate gets into the environment  if and only if the landfill’s capacity to hold liquids is exceeded . This means two things. First, whenever the landfill's capacity is exceeded, some leachate will definitely escape into the environment. Second, if the landfill's capacity is NOT exceeded, then there is nothing to worry about. (Formally, the landfill's capacity being exceeded is both a sufficient and necessary condition for leachate escaping into the environment).

Let's consider choices D and E:

(D) Some landfill leachate is send to sewage treatment plants that are incapable of handling it.

Well, I can see why this is tempting. After all, the last sentence told us that leachate (well, most of it anyways) is sent to sewage treatment plants, and that some sewage treatment plants can't handle leachate. But did we learn whether any leachate goes to the plants that can't hanlde it? Nope. Fine, there may be some plants that can't handle leachate, but it could easily be the case that no leachate is actually sent to these plants--that leachate is only sent to plants that CAN handle leachate.

Thus, choice D could be false, and we can eliminate it.

(E) If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.

Well, we learned that if the landfill's capacity were exceeded that leachate will for sure escape into the environment. So, if no leachate escaped, then capacity was not exceeded (because if capacity were exceeded, leachate would have escaped!). (Many of you will recognize this concept as the "contrapositive").

Thus, choice E must be true (based on the passage). Thus, choice E must be correct.

TAKEWAY: in GMAT inference questions stay very CLOSE to the passage. If you see a choice that must be true, it is undoubtedly the correct answer. If you see a choice that could be false, it is undoubtedly an incorrect answer.

SOMETHING YOU SHOULD KNOW ABOUT THIS QUESTION: this is an LSAT or else an LSAT-like question. It tests formal logic in a way that GMAT CR never would.

Bunuel · Answer

OFFICIAL EXPLANATION

The correct answer choice is (E). The key to this problem is the “if and only if” construction in the second sentence. As mentioned earlier in the chapter, when you encounter that construction, you must respond under the assumption that you will be tested on your knowledge of the relationship produced by that phrase. In this case, the following scenario is produced: CE = the landfill’s capacity to hold liquids is exceeded, LE = leachate escape into the environment. CE<——>LE. According to our knowledge of the double-arrow relationship, only two possible scenarios can result: 1. CE and LE or 2. ~CE and ~LE. You should immediately glance at the question stem and determine what question you are being asked, and then attack the answer choices with the knowledge above. Answer choice (E) reflects scenario 2 above, and (E) is correct.

Answer choice (A): Although leachate escapes in “generally unpredictable” quantities, there is no evidence in the stimulus to suggest that the ability to predict the volume of escaping leachate would help solve the problem. This is a good example of an answer that sounds reasonable or likely to be true, but is incorrect.

Answer choice (B): No. Leachate escapes into the environment if the landfill’s capacity is exceeded, not just if any water permeates a landfill. If the water permeating the landfill caused the capacity to be exceeded then this answer would be correct, but the answer does not indicate that the capacity is exceeded.

Answer choice (C): This is an Exaggerated answer. The stimulus indicates that “not all” sewage plants are capable of handling leachate. The answer choice exaggerates “not all” into none.

Answer choice (D): This is a tricky reworking of the final sentence. The last sentence contains two separate statements, one indicating most landfill leachate is sent to sewage plants and the other revealing that not all sewage plants can handle leachate. But, that does not mean that any leachate is sent to those plants incapable of handling leachate. Thus, answer choice (D) is incorrect.

Answer choice (E): This is the correct answer , and this is the answer you should have been seeking after identifying the “if and only if” in combination with the Must Be True question. Incidentally, when looking for a correct answer in this situation, scenario 2 from the top of the page is more likely to appear than scenario 1 for the simple reason that scenario 2 represents a manipulation of the original statement.

srp · Answer

E

IF X then Y => If NOT Y then NOT X

noboru · Answer

OA is E.
Could anybody clarify why D is incorrect?
Thanks,

dwivedys · Answer

E is a mere paraphrasing of the stimulus --- there is no inference per se here. I dont agree with OA. Also D which I think is right does not imply all sewage plants are incapable of handling leachate as one poster has commented. D says that some leachate goes is sent to sewage treatment plants THAT are incapable of handling it --- using SC knowledge - THAT is a restrictive modifier - so it is talking about THOSE sewage plants that cannot handle leachate. In fact if D had been worded such as - some leachate is sent to sewage treatment plants, WHICH are incapable of handling it --- then it COULD have indicated a possibility that the sewage treatment plants are incapable of handling it.

dwivedys · Answer

Excellent! I am impressed - completely!

I missed the point that the leachates may after all NOT land up at any of the plants incapable of handling them! Gosh!

The other thing that threw me off and which I now remember is having failed to answer a similar question - albeit as I now recollect - was an assumption question - in which one of the (incorrect) answer choices was a paraphrase from the passage - and which I immediately jumped at and selected; turned out it was wrong. That kinda stayed in my memory and now when I saw this question that alarm went off again - because choice E sounded very much like a paraphrase and I felt it was a trap. It is a no brainer practically to see that E is true but well oh well... my bad...

Testluv · Answer

I'm glad you bring this up!

As discussed in my post above, in an inference or must be true type of question, a choice that restates or paraphrases a part of the passage is automatically correct.

However, in an assumption question, a choice that restates evidence is automatically wrong. Why? Because assumptions are, by definition, UNSTATED.

So, we can say:

In assumption questions, choices that restate evidence are automatically incorrect; in inference/must be true, choices that restate evidence are automatically correct.

LogicGuru1 · Answer

ANSWER IS SUPER EASY E

Remembering the definition of inference will help to get the correct answer in under 10 seconds
    (i) Inference is a logical conclusion that can be drawn using one or more premises given in the argument. 
(ii)Also noteworthy is to remember that an inference must never be said or written explicitly in the argument (otherwise it will become just another premise)

E) If leachate does not escape from a landfill into the environment, then the landfill's capacity to hold liquids has not been exceeded.
 We can infer this from the premise in the argument. "If and only if the landfill's capacity to hold liquids is exceeded does the leachates escape into the environment"
 No leaking of leachate=Landfill still have capacity to hold leachate. 
 
CORRECT) Answer is E

anairamitch1804 · Answer

Solutions 1:-

For inference questions we must always be able to prove the answer choice by referring back to the argument. The answers are usually

(1) Paraphrase of one or more of the premises in the argument 
(2) Logical conclusion from one or more premises in the argument

If and only if the landfill's capacity to hold liquids is exceeded does the leachate escape into the environment,

E is nothing but a paraphrase of whats given in the argument i.e using (1) above

but not all sewage plants are capable of handling the highly contaminated water

Choice D is Some landfill leachate is sent to sewage treatment plants that are incapable of handling it.Do we know that leachate has been sent to some sewage plants from whats given in the argument?? NO....

If choice D was

Some sewage treatment plants are incapable of handling the leachate sent to them.-> YES this would be a logical conclusion i.e. using (2) above

Skywalker18 · Answer

There are three claims in this stimulus.

1. If, and only, if the landfill's capacity to hold liquids is exceeded does the leachate escape into the environment.
2. Most landfill leachate is sent directly to sewage treatment plants.
3. Not all sewage plants are capable of handling the highly contaminated water.

We need to find an answer that we can infer from one or more of these statements.

(A) may be true and seems to make sense, but is an unsupported prediction. It may not help solve the problem, however.
(B) contradicts the stimulus. The first claim says that leachate will escape into the environment if, and only if, the landfill's capacity is exceeded - not if leachate permeates a landfill.
(C) is not necessarily true. We know that not all sewage plants are capable of handling the highly contaminated water. That does not mean that no sewage plants are capable of handling leachate.
(D) attempts to combine the second and third statement. However, no inference can be made from combining a SOME statement in the third claim and a MOST statement in the second claim. According to these two claims, it's possible that all leachate is sent directly to only those sewage treatment plants that are capable of handling the contaminated water.
(E) must be true. This is part of what can be inferred from the contrapositive of the first statement.

RohitSaluja · Answer

Answer E and below is the explanation for the same

(A) The ability to predict the volume of escaping landfill leachate would help solve the disposal problem. -  This won't necessarily solve the problem, if we don't develop a new method to fix the issue or even if we rely on sewage treatment plants, we would need to enable them to handle highly contaminated water,

(B) If any water permeates a landfill, leachate will escape into the environment. -  No, water will escape only if the landfill capacity to hold water is excedded

(C) No sewage treatment plants are capable of handling leachate. -  Argument says there are some which can handle

(D) Some landfill leachate is send to sewage treatment plants that are incapable of handling it.  Nothing mentioned for this account

(E) If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.  This is the contrapositive of the condition mention in the argument, hence the answer

CEdward · Answer

Hold on...regarding E), what if the reason why the leachate HAS NOT escaped is that it was sent off to the plants? So maybe it in fact was exceeded...

The passage tells us that IFF the landfill's capacity to hold liquids is exceeded does the leachate escape, but it doesn't preclude the possibility that people could have handled it...

thelastskybender · Answer

Premise: If and only if X   Then Y

Above condition is bidirectional i.e. X is both necessary and sufficient for Y, and Y is both necessary and sufficient for X.

(E) If leachate does not escape from a landfill into the environment, then the landfill’s capacity to hold liquids has not been exceeded.   If -Y then -X: We can infer this because Y is necessary for X. Hence absence of Y will imply absence of X  ]

VerbalBot · Answer

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Leachate is a solution, frequently highly contaminated, that develops

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