#7 - Waste management companies, which collect waste for

[Administrator]

Complete Question Explanation

Weaken—Numbers and Percentages. The correct answer choice is (D)

The structure of the argument, in simplified form, is as follows:

     Premise: Disposable plastics make up an ever‑increasing
     percentage of the waste they handle.

     Conclusion: Attempts to decrease the amount of plastic that
     people throw away in the garbage are failing.

The conclusion is flawed: a numbers conclusion (“amount”) cannot be
drawn solely from percentage information because the overall total could
change dramatically. As you attack the answer choices, look for an answer
that addresses this error.

Answer choice (A): The argument is about how people act when throwing
away garbage, an issue that occurs before the waste management
companies receive the trash. On the other hand, this answer discusses
how the waste management companies dispose of plastics, an issue that
occurs after they have received the waste. Because the two issues occur at
different times in the cycle, this answer does not attack the argument and
is incorrect.

Answer choice (B): Like answer choice (A), this answer raises an issue
that occurs after the waste management companies have received the
waste.

Answer choice (C): This answer addresses how people act prior to
throwing away garbage, but it does not suggest that the amount of plastic
that people throw away is not decreasing. The author would probably
counter this statement by saying that regardless of the fact that people
are more likely to save plastic containers, that tendency is only relative to
glass and metal containers, and people are still throwing away plastics in
an ever-increasing percentage (and thus amount).

Answer choice (D): This is the correct answer. The answer indicates that
the waste management companies no longer receive as much paper, glass,
and metal as they used to. Since this clearly affects the amount of trash
that they process, this would also affect the percentages of each type of
waste. If the amount of paper, glass, and metal drops by a large amount,
the percentage of plastic in the waste would rise even if the actual amount
of plastic waste was reduced. The following example shows how this is
possible:

Capture.PNG

In the example, plastic garbage has risen from 20% to 50%, but the
actual amount of plastic waste has decreased from 20 units to 10 units.
Consequently, because this answer raises a scenario that could disprove
the argument, it is the correct answer.

Answer choice (E): The amount of plastic being manufactured is not the
issue in the stimulus; how much plastic is thrown away is the issue.

In all respects this is a classic numbers and percentages Weaken problem.
Accordingly, we can use this discussion to highlight a general rule for
handling Weaken and Strengthen questions paired with numbers and
percentages stimuli:

     To weaken or strengthen an argument containing numbers
     and percentages, look carefully for information about the total
     amount(s)—does the argument make an assumption based on one
     of the misconceptions discussed earlier?

[voodoochild]

Logical Reasoning » PrepTest 9 - October 1993 LSAT Answers & Explanations - LR » Section #2

I have a quick question.

While solving this question, I thought that a good way to weaken this question would be to say that the 'total number of waste materials' has reduced. However, the correct answer choice talks about the proportion of non-plastic material getting reduced.

Can you please suggest some other ways how we could weaken it?

Here's what I coudl think of:
-Total number of waste materials are getting reduced
-Total number of non-plastic materials are reducing
-Proportion of non-plastic material is reducing (which is actually the answer choice printed above)

The reason why I have asked the above question is that I want to "brainstorm" the number of ways we can weaken these questions.

Your kind reply would be greatly appreciated because I am relatively weak on PErcent/Number problems. Please help me

Appreciate your help. It will help me to grasp %/# concept.


Thanks

[voodoochild]

I received a PM to post the full question. It's from Powerscore Questions by type book - Volume 1 - page 382 #18.

I would appreciate your response. Thanks for helping me..

Thanks

[voodoochild]

Adam,

It's one of the best questions in the Powerscore book - chapter number and percents. I really love your books!

Thanks

[Adam Tyson]

A classic numbers and percentages flaw is that the authors attempt to use a percentage to prove a number or a number to prove a percentage, without providing a crucial piece of information. In order to prove a percentage, you need to have a total and a subtotal - that is, if I know I have 100 marbles and 40 of them are green, I can prove that 40% are green and that 60% are not green. What if I only say that later I get more green marbles - can I prove that my percentage increased? No, not without knowing the new total number of marbles. Maybe I got ten more green marbles, but I also got 90 more that were not green, bringing my total marbles to 200, and reducing the green percentage to 25% (50 out of 200).

Here we know that the percentage (or proportion) of plastic in the landfill went up, and the author concludes that the total amount of plastic did not decrease. Without knowing the total amount of non-plastic in the landfill, we can't prove anything about numbers. Throw some numbers at it, like our marbles: What if we started off with 1000lbs of garbage and half of that was plastic - 500lbs. Later we have 500 lbs of garbage and 80% is plastic - 400lbs. That doesn't match with the author's conclusion, that we haven't reduced the amount of plastic we throw away. It does match with our correct answer - the non-plastics dropped from 50% to 20%.

In short, to weaken a numbers and percentages question like this one, suggest that there is an alternate explanation for the changing percentage (not unlike weakening a cause-and-effect question, which this is, sort of - the author argues that a cause did not lead to an effect, and our answer suggests that it may have).

If we try to weaken by saying that the total amount of plastic has decreased, we would be right, but is that the best way? Without explaining how that could happen (as the correct answer does), it may weaken, but not very well. Weaken questions require that you pick the one that weakens the most, and the correct answer here does that better by including the explanation (that the proportion of non-plastics went down).

Hope that helped!

Adam M. Tyson
PowerScore LSAT Instructor

[voodoochild]

thanks for your reply, Adam.

I have a basic question - I agree with you that if the total goes down, the argument would be weakened. However, if Total = Plastic +non-plastic and assuming that the total went down, there are two possibilities that Plastic would go down, something we want in order to weaken the argument, or non-plastic went down, or both of them went down.

(*went down* = the number went down)

So, my question is that how does a decreasing total translate to decreasing proportion of non-plastic material. I can think of an example in terms of numerical terms. For instance,

Total - 100
Plastic =40
non-plastic = 60

New :
total = 20
Plastic = 10
Non-plastic = 10

Now, Non-plastic % = 50%; # of Plastic has decreased even though the proportion is high. But it would be really difficult to do the above computation in less than a minute. I am looking for an intuitive way to think about the above logic. Essentially, I am not able to understand (Total : Down ==> Decreasing % of non-plastic material ) in terms of Percentage = (Amount/Total), in other words, in more intuitive way.

Can you please help me to fill the gap?

Thanks

[Adam Tyson]

A decreasing total weakens the argument not because it guarantees less plastic, but because it calls into question the conclusion that plastic did not decrease. The argument's conclusion may still be a good one - the author may be right. When we weaken an argument, we don't have to destroy it, but only show that it is not so strong as the author may think. With more data we may be able to destroy the conclusion, or we may be able to strengthen it or even prove it is correct, but for now we can weaken it just by calling out the flaw. A decreasing proportion of non-plastic in the landfill gives us a reason to question the author's conclusion, without totally destroying it.

The very fact that our new piece of information leads to at least two different conclusions (as you demonstrated) shows that it weakens the argument, because it makes each possible conclusion less certain. Doubt = weaken.

The short answer is, when given only percentages, numbers cannot be proved. To weaken an argument like that, point that out, perhaps by suggesting that the totals may have changed, making the percentages take on different meaning.

[voodoochild]

Thanks Adam for your reply. I think what I was confused about was : how can i *predict* intuitively that given Total = Plastic + non-plastic, proportion of plastic is decreasing, and for the # of plastic to go down, the proportion of non-plastic *could* go down. I see that, in one of the instances, author's argument is weakened. However, I cannot be expected to compute such math in under 1 minute. Correct? Any tips or ideas to come up with such answers intuitively? At first, I didnt realize that if the proportion of non-plastic goes down, the number of plastic material *could* go down. I had to think of an example mathematically.

[Dave Killoran]

Hi Voodoo,

These problems don't actually require you to compute any math. The problems all occur under a general framework where you are expected to understand the range of relationships and resulting possibilities. So, it's not about predicting or computing, but rather understanding what can occur in #% scenarios. This is the value of prior preparation: you learn about these types of situations, so if you encounter them later, you've already considered what can occur. For example, in the LRB, in the #%s chapter, I specifically note that a rising percentage doesn't necessarily translate into a rising number. Considering/understanding that possibility (and what happens to the components that make up the other percentages, as well as the total) is critical to quickly solving a problem like this.

That said, this still isn't an easy question, but, underneath, it trades on classic #% ideas. The studying and discussion you are doing now will help you solve these problems when you encounter them in the future. A suggestion: go back to that chapter in the LRB, and look at the scenarios discussed. Then, in each, consider what could occur and not occur, as well as what would need to occur in order to force certain results. Consider also what would happen to the "other" players in the scenario (the other percents, or the other numbers).

Let me know if that helps. Thanks!

[sunshine123]

Howdy,

Could yall expand on why E is incorrect? If the percentage of products using plastic packaging is increasing, that may translate to more plastic and consequently more plastic being disposed of -- this much seems to me like a certain possibility. It is reasoning that relies on an assumption(or number of them). Is that also why it is wrong?

Best,
Dylan Ramirez