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Tough & Tricky CR Prep question

by Mo2men » Wed Aug 10, 2016 11:16 am

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From 1978 to 1988, beverage containers accounted for a steadily decreasing percentage of the total weight of household garbage in the United States. The increasingly widespread practice of recycling aluminum and glass was responsible for most of this decline. However, although aluminum recycling was more widely practiced in this period than glass recycling, it was found that the weight of glass bottles in household garbage declined by a greater percentage than the weight of aluminum cans.

Which of the following, if true of the United States in the period 1978 to 1988, most helps to account for the finding?

(A) Glass bottles are significantly heavier than aluminum cans of comparable size.
(B) Recycled aluminum cans were almost all beverage containers, but a significant fraction of the recycled glass bottles had contained products other than beverages.
(C) Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.
(D) The total weight of glass bottles purchased by households increased at a slightly faster rate than the total weight of aluminum cans.
(E) In many areas, glass bottles had to be sorted by color of the glass before being recycled, whereas aluminum cans required no sorting.

I do not understand how C is correct? there is no mention about plastic in the prompt.

Why A is wrong??
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by MartyMurray » Wed Aug 10, 2016 2:03 pm

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A is a trap answer. It seems to explain why the percentage weight of glass bottles changed more but actually does not.

Think of it this way, if the number of glass bottles went down by 10% and the number of aluminum cans went down by 10%, the weights of the bottles and cans would both decrease by 10% even though the bottles weight more.

So the fact that the bottles weigh more does not explain why the total weight of the bottles decreased by a percentage greater than the percentage decrease in the total weight of the cans.

C on the other hand shows another way that the glass bottles ENDING UP IN HOUSEHOLD GARBAGE decreased. Not only were they being recycled, but also manufacturers were reducing their use of glass, and using plastic instead.

So even though aluminum recycling was more widely practiced than glass recycling, the amount of glass was ending up in household garbage decrease by a greater percentage than the amount aluminum did, because glass bottle use was reduced.
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by GMATGuruNY » Thu Aug 11, 2016 2:53 am

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Mo2men wrote:From 1978 to 1988, beverage containers accounted for a steadily decreasing percentage of the total weight of household garbage in the United States. The increasingly widespread practice of recycling aluminum and glass was responsible for most of this decline. However, although aluminum recycling was more widely practiced in this period than glass recycling, it was found that the weight of glass bottles in household garbage declined by a greater percentage than the weight of aluminum cans.

Which of the following, if true of the United States in the period 1978 to 1988, most helps to account for the finding?

(A) Glass bottles are significantly heavier than aluminum cans of comparable size.
(B) Recycled aluminum cans were almost all beverage containers, but a significant fraction of the recycled glass bottles had contained products other than beverages.
(C) Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.
(D) The total weight of glass bottles purchased by households increased at a slightly faster rate than the total weight of aluminum cans.
(E) In many areas, glass bottles had to be sorted by color of the glass before being recycled, whereas aluminum cans required no sorting.
Fact 1: Glass recycling is less widely practiced than aluminum recycling.
Fact 2: The weight of glass bottles in household garbage declined by a greater percentage than the weight of aluminum cans.

The correct answer choice must explain how the weight of glass bottles in garbage declined by a greater percentage than the weight of aluminum cans, even though glass recycling is less widely practiced.

Answer choice C: Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.
Since products previously sold in glass bottles are now sold in plastic containers, households have FEWER GLASS BOTTLES -- explaining how the weight of glass bottles in household garbage decreased, despite the lack of glass recycling.

The correct answer is C.
I do not understand how C is correct? there is no mention about plastic in the prompt.
Correct answers to resolve/explain problems ALWAYS offer new information not discussed in the prompt.
Do not eliminate an answer choice simply because it mentions something not discussed in the passage.
Why A is wrong?
A: Glass bottles are significantly heavier than aluminum cans of comparable size.

Here, glasses weigh more than cans, but -- in accordance with the passage -- it must still be true that aluminum recycling is more widely practiced than glass recycling.
Consider the following case:
Average aluminum can weight = 10 ounces, average glass bottle weight = 100 ounces.
In 1978, the average household discards 10 cans (for a total of 100 ounces) and 10 bottles (for a total of 1000 ounces).
In 1998, the average household recycles 8 cans (decreasing its can refuse by 80 ounces) and 2 glasses (decreasing its glass refuse by 200 ounces).
Percent decrease in the can weight = (80-ounce decrease)/(100-ounce original total weight) = 80%.
Percent decrease in the glass bottle weight = (200-ounce decrease)/(1000-ounce original total weight) = 20%.
Result:
The weight of the glass bottles decreases by a SMALLER percentage than the weight of the aluminum cans.
Thus, A does NOT explain how the weight of glass bottles in household garbage decreased by a greater percentage than the weight of aluminum cans.
Eliminate A.
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by Mo2men » Thu Aug 11, 2016 4:58 am

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GMATGuruNY wrote:
Why A is wrong?
A: Glass bottles are significantly heavier than aluminum cans of comparable size.

Here, glasses weigh more than cans, but -- in accordance with the passage -- it must still be true that aluminum recycling is more widely practiced than glass recycling.
Consider the following case:
Average aluminum can weight = 10 ounces, average glass bottle weight = 100 ounces.
In 1978, the average household discards 10 cans (for a total of 100 ounces) and 10 bottles (for a total of 1000 ounces).
In 1998, the average household recycles 8 cans (decreasing its can refuse by 80 ounces) and 2 glasses (decreasing its glass refuse by 200 ounces).
Percent decrease in the can weight = (80-ounce decrease)/(100-ounce original total weight) = 80%.
Percent decrease in the glass bottle weight = (200-ounce decrease)/(1000-ounce original total weight) = 20%.
Result:
The weight of the glass bottles decreases by a SMALLER percentage than the weight of the aluminum cans.
Thus, A does NOT explain how the weight of glass bottles in household garbage decreased by a greater percentage than the weight of aluminum cans.
Eliminate A.
Should not we say the following:

decline in Aluminium = (100-80)/100 = 20%

decline in glass = (1000=200)/1000= 80%

hence the decline in Glass was greater than decline in Aluminium as stated in prompt.

Thanks
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by GMATGuruNY » Thu Aug 11, 2016 6:05 am

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Mo2men wrote:Should not we say the following:

decline in Aluminium = (100-80)/100 = 20%

decline in glass = (1000=200)/1000= 80%

hence the decline in Glass was greater than decline in Aluminium as stated in prompt.

Thanks
A container is either DISCARDED in the household garbage or RECYCLED.
Thus, in the case above:
The 8 10-ounce aluminum cans that are recycled are NOT discarded in the household garbage.
As a result, the weight of aluminum in the household garbage decreases by 80 ounces (80% of the original weight of 100 ounces).
The 2 100-ounce glass bottles that are recycled are NOT discarded in the household garbage.
As a result, the weight of glass in the household garbage decreases by 200 ounces (20% of the original weight of 1000 ounces).
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by Mo2men » Thu Aug 11, 2016 6:57 am

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GMATGuruNY wrote:
A container is either DISCARDED in the household garbage or RECYCLED.
Thus, in the case above:
The 8 10-ounce aluminum cans that are recycled are NOT discarded in the household garbage.
As a result, the weight of aluminum in the household garbage decreases by 80 ounces (80% of the original weight of 100 ounces).
The 2 100-ounce glass bottles that are recycled are NOT discarded in the household garbage.
As a result, the weight of glass in the household garbage decreases by 200 ounces (20% of the original weight of 1000 ounces).
Thanks Mitch for your great example and last note about difference between discard and recycle. I discovered that I was treating the prompt as 'discard'. it is now evident that over years glass bottles gradually disappear from garbage due to plastic bottle replacement.
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by ResilientSoul » Sat Oct 01, 2016 2:30 am

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I want to understand why B is wrong better.

I rephrased the argument as follows

Garbage DUE TO beverage containers declined. Recycling of glass and aluminium was identified as a cause.
Also Recycling of aluminium was more popular than recycling of glass(Ideally it should follow that % of aluminium in garbage should decline more since more of the aluminium stuff is being recycled).
However glass bottles in household garbage declined by a greater % than the weight of the aluminium cans.

As i understand the reason B is wrong is because the argument is solely concerned with decline in garbage DUE TO beverage containers.
Answer choice B is telling us that recycled glass consisted of beverage containers + glass containers that contained products OTHER THAN BEVERAGES

Since we are looking to explain a lower decline in garbage due to glass beverage containers only , recycling of glass containers which contained products other than beverages is out of scope and hence B is wrong

Is my reasoning to omit B valid?
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by GMATGuruNY » Sat Oct 01, 2016 3:25 am

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ResilientSoul wrote:I want to understand why B is wrong better.

I rephrased the argument as follows

Garbage DUE TO beverage containers declined. Recycling of glass and aluminium was identified as a cause.
Also Recycling of aluminium was more popular than recycling of glass(Ideally it should follow that % of aluminium in garbage should decline more since more of the aluminium stuff is being recycled).
However glass bottles in household garbage declined by a greater % than the weight of the aluminium cans.

As i understand the reason B is wrong is because the argument is solely concerned with decline in garbage DUE TO beverage containers.
Answer choice B is telling us that recycled glass consisted of beverage containers + glass containers that contained products OTHER THAN BEVERAGES

Since we are looking to explain a lower decline in garbage due to glass beverage containers only , recycling of glass containers which contained products other than beverages is out of scope and hence B is wrong

Is my reasoning to omit B valid?
(B) Recycled aluminum cans were almost all beverage containers, but a significant fraction of the recycled glass bottles had contained products other than beverages.

It is stated as a FACT that glass recycling was less widely practiced than aluminum recycling.
What the glass containers held prior to recycling is irrelevant.
The correct answer must explain why the weight of glass bottles in garbage declined by a greater percentage than the weight of aluminum cans, even though glass recycling was less widely practiced.
Eliminate B.
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by MartyMurray » Sat Oct 01, 2016 3:27 am

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ResilientSoul wrote:I want to understand why B is wrong better.

I rephrased the argument as follows

Garbage DUE TO beverage containers declined. Recycling of glass and aluminium was identified as a cause.
Also Recycling of aluminium was more popular than recycling of glass(Ideally it should follow that % of aluminium in garbage should decline more since more of the aluminium stuff is being recycled).
However glass bottles in household garbage declined by a greater % than the weight of the aluminium cans.

As i understand the reason B is wrong is because the argument is solely concerned with decline in garbage DUE TO beverage containers.
Answer choice B is telling us that recycled glass consisted of beverage containers + glass containers that contained products OTHER THAN BEVERAGES

Since we are looking to explain a lower decline in garbage due to glass beverage containers only , recycling of glass containers which contained products other than beverages is out of scope and hence B is wrong

Is my reasoning to omit B valid?
I find that your reasoning is not sufficiently robust.

Notice, the OA is about plastic containers, but the OA answers the question. So eliminating an answer choice because it focuses on something not discussed in the prompt is not really an effective method. In fact, I have seen people eliminate the right answer first via using "This is not mentioned in the prompt" type thinking.

You can do better by more clearly identifying why the information provided by B does not answer the question. Does the fact that some of the recycled bottles had contained non beverage products answer the question? What does its presence change or not change?

What are the key points of the argument? Does this fact affect any of those points?

Also, noticing key details is key for getting CR questions right.

Did you notice that B is about recycled aluminum and glass only? Does that detail matter?

Also, did you notice that the conclusion of the argument does not include the word beverage? Does that detail make B somehow more relevant than you thought it to be?

There are clear, logical reasons why B does not answer the question. By identifying them, you will arrive at a more robust reason for eliminating B.
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by ResilientSoul » Sat Oct 01, 2016 10:12 am

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I find that your reasoning is not sufficiently robust.
Notice, the OA is about plastic containers, but the OA answers the question. So eliminating an answer choice because it focuses on something not discussed in the prompt is not really an effective method. In fact, I have seen people eliminate the right answer first via using "This is not mentioned in the prompt" type thinking.
I agree with you completely on this. I did not eliminate C because it looked irrelevant but because it doesn't say that consumers actually bought the plastic bottles -- It just says that Manufacturers replaced glass bottles with plastic containers.
In the hindsight i do realise that this was flawed reasoning since it really doesn't matter whether the users bought the plastic bottles or not (anyways the glass bottles are certain to decline as long as manufacturers are not manufacturing them)
You can do better by more clearly identifying why the information provided by B does not answer the question. Does the fact that some of the recycled bottles had contained non beverage products answer the question? What does its presence change or not change?
The fact that some of the recycled bottles had contained non beverage products does not impact anything here. The argument is very specific about decline in beverage glass bottles in the garbage hence non beverage glass bottles is irrelevant. Do you agree?

What are the key points of the argument? Does this fact affect any of those points?

Also, noticing key details is key for getting CR questions right.
Did you notice that B is about recycled aluminum and glass only? Does that detail matter?
This is a good catch . I almost ignored this. The recycled aluminium and glass doesn't matter here since the argument is concerned about less glass in the garbage
Also, did you notice that the conclusion of the argument does not include the word beverage? Does that detail make B somehow more relevant than you thought it to be?
I agree that the conclusion doesn't explicitly state the word beverage but isn't the argument on the whole talking about the decreasing percentage of beverage containers(aluminium+glass) in the household garbage?
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by RBBmba@2014 » Mon Oct 03, 2016 3:27 am

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GMATGuruNY wrote:
Why A is wrong?
A: Glass bottles are significantly heavier than aluminum cans of comparable size.

Here, glasses weigh more than cans, but -- in accordance with the passage -- it must still be true that aluminum recycling is more widely practiced than glass recycling.
Consider the following case:
Average aluminum can weight = 10 ounces, average glass bottle weight = 100 ounces.
In 1978, the average household discards 10 cans (for a total of 100 ounces) and 10 bottles (for a total of 1000 ounces).
In 1998, the average household recycles 8 cans (decreasing its can refuse by 80 ounces) and 2 glasses (decreasing its glass refuse by 200 ounces).
Percent decrease in the can weight = (80-ounce decrease)/(100-ounce original total weight) = 80%.
Percent decrease in the glass bottle weight = (200-ounce decrease)/(1000-ounce original total weight) = 20%.
Result:
The weight of the glass bottles decreases by a SMALLER percentage than the weight of the aluminum cans.
Thus, A does NOT explain how the weight of glass bottles in household garbage decreased by a greater percentage than the weight of aluminum cans.
Eliminate A.
Hi GMATGuruNY,
After going through your above data-driven analysis, I can understand why A is wrong.

But the point is this sort of data analysis, I guess, will NOT be doable during test environment under time constraint, therefore can you please explain how EXACTLY we can quickly determine that A is wrong without even going through such data analysis ?
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by RBBmba@2014 » Thu Oct 20, 2016 10:11 am

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Hi GMATGuruNY,
Any update on the above concerns Sir ?

Look forward to hear from you! Much thanks in advance.
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by jabhatta » Sat Mar 24, 2018 1:39 pm

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GMATGuruNY wrote:
Mo2men wrote:From 1978 to 1988, beverage containers accounted for a steadily decreasing percentage of the total weight of household garbage in the United States. The increasingly widespread practice of recycling aluminum and glass was responsible for most of this decline. However, although aluminum recycling was more widely practiced in this period than glass recycling, it was found that the weight of glass bottles in household garbage declined by a greater percentage than the weight of aluminum cans.

Which of the following, if true of the United States in the period 1978 to 1988, most helps to account for the finding?

(A) Glass bottles are significantly heavier than aluminum cans of comparable size.
(B) Recycled aluminum cans were almost all beverage containers, but a significant fraction of the recycled glass bottles had contained products other than beverages.
(C) Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.
(D) The total weight of glass bottles purchased by households increased at a slightly faster rate than the total weight of aluminum cans.
(E) In many areas, glass bottles had to be sorted by color of the glass before being recycled, whereas aluminum cans required no sorting.
Fact 1: Glass recycling is less widely practiced than aluminum recycling.
Fact 2: The weight of glass bottles in household garbage declined by a greater percentage than the weight of aluminum cans.

The correct answer choice must explain how the weight of glass bottles in garbage declined by a greater percentage than the weight of aluminum cans, even though glass recycling is less widely practiced.

Answer choice C: Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.
Since products previously sold in glass bottles are now sold in plastic containers, households have FEWER GLASS BOTTLES -- explaining how the weight of glass bottles in household garbage decreased, despite the lack of glass recycling.

The correct answer is C.
I do not understand how C is correct? there is no mention about plastic in the prompt.
Correct answers to resolve/explain problems ALWAYS offer new information not discussed in the prompt.
Do not eliminate an answer choice simply because it mentions something not discussed in the passage.
Why A is wrong?
A: Glass bottles are significantly heavier than aluminum cans of comparable size.

Here, glasses weigh more than cans, but -- in accordance with the passage -- it must still be true that aluminum recycling is more widely practiced than glass recycling.
Consider the following case:
Average aluminum can weight = 10 ounces, average glass bottle weight = 100 ounces.
In 1978, the average household discards 10 cans (for a total of 100 ounces) and 10 bottles (for a total of 1000 ounces).
In 1998, the average household recycles 8 cans (decreasing its can refuse by 80 ounces) and 2 glasses (decreasing its glass refuse by 200 ounces).
Percent decrease in the can weight = (80-ounce decrease)/(100-ounce original total weight) = 80%.
Percent decrease in the glass bottle weight = (200-ounce decrease)/(1000-ounce original total weight) = 20%.
Result:
The weight of the glass bottles decreases by a SMALLER percentage than the weight of the aluminum cans.
Thus, A does NOT explain how the weight of glass bottles in household garbage decreased by a greater percentage than the weight of aluminum cans.
Eliminate A.
Hi Mitch - when I read option A .... I actually thought A was referring to 1 unit of a glass bottle is significant heavier than 1 aluminium can

In your analysis, it seems like you thought A was referring to the total weight of glass bottles vs the total weight of aluminium cans

As a test taker, how do you know what the test is referring to (one single unit of glass or aluminum or total weight of glass or total weight of aluminium)

Please assist !
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