#12 - Leachate is a solution, frequently highly contaminated

[Administrator]

Complete Question Explanation

Must Be True—SN. The correct answer choice is (E)

This tricky stimulus presents a rare, but highly predictable, conditional relationship: “if and only if.” This unusual wording includes both a sufficient (“if”) and a necessary (“only if”) condition, and thus creates a double-arrow between the two terms. Note: the phrase “if, but only if” yields the same double-arrow relationship.

More specifically, this stimulus begins by introducing leachate and describing how it forms. We are told that if and only if the landfill’s capacity to hold liquids is exceeded will leachate escape into the environment. This appears as:

• Capacity Exceeded Leachate Escapes

The contrapositive of this statement can be diagrammed as:

• Capacity Exceeded Leachate Escape

Finally, the stimulus concludes by describing potential problems with the disposal of leachate, saying that not all sewage plants are capable of handling the highly contaminated water.

Because of the unusual nature of the double-arrow produced here, the most obvious inference (and prephrase) comes from the contrapositive. Hence you should look for an answer choice exploiting this relationship.

Answer choice (A): There is no information in the stimulus about what effect the ability to predict the volume of escaping leachate would have in helping to solve the disposal problem.

Answer choice (B): Leachate develops when water permeates a landfill, and if that landfill’s capacity to hold liquids is exceeded that leachate escapes into the environment, but there is no direct connection between water permeating a landfill and leachate escaping. This is a tempting answer choice but it is ultimately wrong because it attempts to connect two terms in a way that cannot be definitively known from the stimulus.

Answer choice (C): We are only told that “some” sewage treatment plants cannot properly handle leachate. It is still possible that “some” can.

Answer choice (D): The stimulus states that some sewage plants cannot handle leachate, but we do not know that any landfill leachate is actually sent there. This answer choice makes an assumption that is not fully supported by the stimulus.

Answer choice (E): This is the correct answer choice. As mentioned previously, the most significant inference comes from the contrapositive of th

[ellenb]

Dear Powerscore,


So, I looked at the answer choices and the explanations on the online center, but I am still confused as to why answer choice D is incorrect, in the stimulus it says most landfill leachate is sent directly to sewage treatment plants. And I know that most can mean some, thus some leachate can be sent to sewage treatment plants. Thus, I am mostly confused about that.

When I say for example: , I will have most of the strawberies, it could also mean that I will have some of the strawberies, that is true correct? since most can go down to some.

Thanks in advance,

Ellen

[Ron Gore]

Hi, Ellen!

Thanks for your question.

First, this is a Must Be True question. So, the Prephrase is that the correct answer may be either a restatement of one of the facts in the stimulus or an inference that is permissible from a combination of those facts.

Answer choice (D) is indeed a tricky, attractive incorrect answer choice. It takes advantage of the last two facts you received: (1) most landfill leachate is sent directly to sewage treatment plants; and (2) not all sewage plants are capable of handling the highly contaminated water.

To select answer choice (D), you would need to combine these to facts to infer that some leachate is actually sent to a sewage treatment plant that can't handle it. However, while this is a possibility, something that could be true, it is not something that Must Be True. For all we know, the leachate is only being sent to those treatment plants that can handle it. Since it is only a could be true inference, it is incorrect.

In your example about strawberries, you are correct that if you are given the statement, "I will have most of the strawberries," that statement inherently contains the idea "I will have some of the strawberries." However, to make your example analogous to the stimulus, we would need two separate statements.

For example: (1) most strawberries are sent directly an individual; and (2) not all individuals are capable of eating the strawberries. In this example, we wouldn't know whether any of the strawberries actually were sent to an individual that could not eat them.

I hope this helps. Please let me know if I can be of further assistance.

Thanks!

Ron

[ellenb]

Thanks Ron,

So, how do we know that leachate is sent to the facilities that are able to handle it? How did you come up with the statement below.

"For all we know, the leachate is only being sent to those treatment plants that can handle it. "


Thanks

Ellen

[Ron Gore]

Hi Ellen,

The whole point is that it is not clear to which treatment plant the sewage is sent. It might have been sent to a plant that could handle it, or it might have been sent to a plant that cannot handle it. That uncertainty is why answer choice (D) is incorrect as answer to this Must Be True question.

The phrase I used in my initial response to you, "...for all we know," is a colloquialism used to express that kind of uncertainty.

Ron

[ellenb]

Dear Powerscore,

I have read the explanations for the following question about Leachate, however I am a bit confused about answer choice D.
It says in the explanations that we cannot make the assumption that the Leachate is sent to the sewage for sure. However, in the stimulus it says that most landfill Leachate is sent directly to the sewage treatment plants. So, in a way we do know that if most lanfill leachate is sent to the sewage treatment plants than we can have some leandfill leachate sent to sewage treatment plants.
Please let me know if my thought process is correct as I seem a bit confused, because I know that most can be some.

Thanks

Ellen

[Ron Gore]

Hi Ellen,

As to answer choice (D), the stimulus does not tell us whether any of the leachate is sent to a sewage treatment plant that is incapable of handling it. And, unfortunately, the most/some analysis is inapplicable to this answer choice.

It appears that the mistake you are making is failing to distinguish between those plants that can handle leachate and those that cannot. The stimulus tells us that most of the leachate is sent directly to sewage treatment plants, and so we inherently know that some of the leachate is sent to sewage treatment plants. But this inherent most/some inference does not tell us to which plants the sewage is sent.

We know that most of the leachate is sent to a treatment plant. And let's assume that there are 10 treatment plants. The stimulus says that "not all" treatment plants can handle leachate. ("Not all" is not the same as "some." I'll refer you to pages 2-1 and 2-2 of the lesson to review the distinction between those two terms.) So, let's say that 1 out of the 10 treatment plants is incapable of handling leachate. Nothing in the stimulus tells us that any of the leachate goes to that one particular plant that cannot handle it. While it is possible, we cannot state definitively that the 1 incapable plant receives any of the leachate.

Please let me know if I can be of further assistance.

Thanks,

Ron

[ellenb]

Dear Ron,

If I am understanding it correctly,

It is just like saying: most of the plants in the garden get watered daily.

Some cannot handle lots of water.


And the conclusion: just connects the two statements (assuming that the plants that will get watered will not be able to handle it).

So, if I have 10 plants, and I water 9 of the 10. Than I assumed that the ones I will be watered will not be able to handle lots of water. However, maybe I have 9 plants that can handle lots of water and 1 that cannot handle water. And the stimulus assumed that the one that when I said most, I have included the plant that cannot handle lots of water, however, it might be the case just like the stimulus that the plant that cannot handle water I do not water. The same as in the stimulus the plants that are incapable of handling sewage is not sent any leachate.

Basically the statements that are in the stimulus are two separate statements and what the test makers want us to make is relationships that are not there, which i did the first time around.

When we see: most landfill leachate is sent directly to sewage plants,

and

Some plants are not able to handle it.

I linked them incorrectly or assumed there is a relationship that is not there which says:
Most landfill leachate that is sent will go to the sewage plants that will not be able to handle it.


However, it is not necessarily true, that the plants that cannot handle it will get leachate.
And this is I think were I went wrong. Or in my example, I assume that the plants that cannot handle lots of water will be watered, however it might be or it might be not.

I guess it is similar to the logic games where test makers want us to make relationships that are not there.

Please take a lot, and please let me know if I make sense, I might have repeated myself, but I just want to make sure that I got your point.

Thanks in advance!

Ellen

[Ron Gore]

I linked them incorrectly or assumed there is a relationship that is not there which says:
Most landfill leachate that is sent will go to the sewage plants that will not be able to handle it.

However, it is not necessarily true, that the plants that cannot handle it will get leachate.
And this is I think were I went wrong.

You're exactly right, Ellen, and it's great to see that you've got it! You're also correct in saying that Law Services hopes that you'll make improper connections throughout the test, and not just in the Games section.

Best Wishes,

Ron

[salty]

Hi,

In this question, the answer shows to be (E). But this is only a contrapositive of "IF the landfill's capacity to hold liquid exceeds, the leachate escapes". Whereas in the question passage, it says "IF and ONLY IF the landfill's capacity exceeds", introducing as both sufficient and necessary. So I thought the answer choice (E) would not be valid because it's only half correct.
Can anyone please explain? Thank you.