From 2000 to 2010, beverage containers accounted for a steadily decrea

Question

From 2000 to 2010, beverage containers accounted for a steadily decreasing percentage of the total weight of domestic garbage in Brazil. The increasingly widespread practice of recycling aluminum and plastic was responsible for most of this decline. However, although aluminum recycling was more widely practiced in this period than plastic recycling, the total weight of plastic bottles in Brazil’s domestic garbage declined by a greater percentage during this time than the total weight of aluminum cans in Brazil’s domestic garbage.
 
Which of the following, if true in Brazil from 2000 to 2010, most helps to account for the apparent discrepancy?

(A) Consumers increasingly favored glass beverage containers over plastic ones.

(B) Plastic bottles were significantly heavier than aluminum cans of comparable size.

(C) Most recycled aluminum cans were beverage containers, but a significant fraction of recycled plastic bottles were not beverage containers.

(D) The total weight of plastic bottles purchased by Brazilians increased at a slightly faster rate than did the total weight of aluminum cans purchased by Brazilians.

(E) In Brazil, the total number of plastic bottles recycled between 2000 and 2010 was less than the total number of aluminum cans recycled during that time.

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GMATNinja · Accepted Answer

First, let's identify the "apparent discrepancy" in the question.

We know that from 2000 to 2010, beverage containers accounted for a steadily decreasing percentage of the total weight of domestic garbage in Brazil, thanks primarily to "the increasingly widespread practice of recycling aluminum and plastic." We also know that aluminum recycling was more widely practiced in this period than plastic recycling. So it would seem that the weight of aluminum in domestic garbage would decline faster.

But here's the discrepancy: the opposite seems to be true. "...the total weight of plastic bottles in Brazil’s domestic garbage declined by a greater percentage during this time than the total weight of aluminum cans in Brazil’s domestic garbage."

So we need to find something that will help us explain why the total weight of plastic bottles declined by a greater percentage than the weight of aluminum cans -- despite the fact that aluminum recycling was more widespread during this period.

At first glance, this might seem to be out of scope, since the passage doesn't mention glass at all. But (A) is basically telling us that recycling might not be the only factor reducing the amount of aluminum in Brazil's garbage. If consumers increasingly favored glass beverage containers over plastic ones, that would reduce the number of plastic beverage bottles used by Brazilians and thus reduce the weight of plastic in Brazil's garbage.

In other words, plastic recycling may not have significantly reduced the weight of plastic in Brazil's garbage, but the change in Brazilians' preferences may have significantly reduced the weight of plastic in Brazil's garbage. This potentially explains why the percent decrease in weight was higher for plastic bottles than for aluminum cans, so let's hang on to choice (A).

Absolutely everything in the questions deals with percentages, so the relative weight of different containers is irrelevant. Choice (B) does not explain the apparent discrepancy.

This statement gives us another reason to expect the percent decrease in the weight of aluminum cans to be GREATER than the percent decrease in the weight of plastic bottles. If the opposite information were given (i.e. that a significant fraction of aluminum cans were not beverage containers and most recycled plastic bottles were beverage containers), that  might  help explain the discrepancy. The statement given in choice (C) only makes the discrepancy more glaring.

This statement also makes the discrepancy more glaring. If plastic recycling is less widespread AND Brazilians are using more plastic bottles, we would certainly expect the weight of aluminum cans to decrease by a larger percentage. If we were told that the total weight of aluminum cans purchased by Brazilians increased at a significantly faster rate than did the total weight of plastic bottles, that might explain the discrepancy; however, the statement given in choice (D) does not explain the discrepancy.

We don't care about the number of bottles or cans, only about the total weight as a percentage of the total domestic garbage. Statement (E) does not help.

Choice (A) is the best answer.

KarishmaB · Answer

Beverage containers/Total Garbage is decreasing - because aluminium and plastic are being recycled. So if it was 20% before, it is 10% now.

Aluminium recycling was more widely practiced than plastic recycling.

But "plastic bottles weight/total garbage weight" reduced more than "aluminium can weight/total garbage weight".
So say if "plastic bottles weight/total garbage weight" was 5%, it has come down to 2% while "aluminium can weight/total garbage" weight has come down from 5% to only 4%. More reduction in plastic weight.

Discrepancy - Though aluminium recycling is more popular, plastic beverage weight has come down more.

It seems that there is something other than recycling too that is reducing the plastic. Let's look at the options.

(A) Consumers increasingly favored glass beverage containers over plastic ones.

This is the answer. It tells us why plastic beverage weight is coming down more than aluminium weight. Plastic is being replaced by glass. So perhaps the plastic weight is going down from 5% to 3% because of that. Then from 3%, it is going down to 2% because of recycling.

(B) Plastic bottles were significantly heavier than aluminum cans of comparable size.

We don't know the terms in which we measure "aluminium recycling is more popular than plastic recycling" - is it units recycled or weight recycled. Hence, this statement does not explain the paradox.

(C) Most recycled aluminum cans were beverage containers, but a significant fraction of recycled plastic bottles were not beverage containers.

This is irrelevant. Note what our paradox is: Though aluminium recycling is more popular than plastic recycling, "plastic bottles weight/total garbage weight" reduced more than "aluminium can weight/total garbage weight".
What part of plastic bottles constituted beverage containers and what part of aluminium cans constituted beverage containers is irrelevant to our paradox. The weight of each is being compared with total garbage weight. The sentence about beverage containers reducing is given as context only.

(D) The total weight of plastic bottles purchased by Brazilians increased at a slightly faster rate than did the total weight of aluminum cans purchased by Brazilians.

With aluminium recycling being more popular and rate of buying aluminium being lesser, aluminium should have decreased by a greater percentage in the total garbage as compared with plastic. It doesn't resolve the paradox, it instead makes it more unlikely.

(E) In Brazil, the total number of plastic bottles recycled between 2000 and 2010 was less than the total number of aluminum cans recycled during that time.

If fewer plastic bottles were recycled as compared with number of aluminium cans, aluminium cans should have decreased by a greater percentage in the total garbage as compared with plastic bottles. It doesn't resolve the paradox, it instead makes it more unlikely.

Answer (A)

deep14 · Answer

IMO A.

A. CORRECT. If plastic bottles are ditched in favor of some other material then less tonnage of plastic garbage will be available.
B. INCORRECT. If this is true then it should have been true in past also and hence doesn't explain why there is a sudden drop in plastic garbage.
C. IRRELEVANT. We are concerned with beverage cans.
D. INCORRECT. Same argument as B plus people buying more plastic doesn't automatically prove that they are recycling more.
E. INCORRECT. % increase in no of plastic < % increase in no of Al doesn't prove that % change weight of P < % change in weight of Al recycled.

spetznaz · Answer

Phew this one was a tough one .. My take on this one :

Premise :

1) % of beverage containers in domestic waste has been decreasing over a period from 2000 to 2010. Recycling was responsible for this trend. 
2) Aluminum recycling was more widely practiced in this period than plastic recycling,

Conclusion :

The total weight of plastic bottles in Brazil’s domestic garbage declined by a greater percentage during this time than the total weight of aluminum cans in Brazil’s domestic garbage.

This is a paradox question.

Pre-think : We need to find out why the total weight of plastic bottles in garbage declined by a greater % than the decline in total weight of aluminum cans in spite of greater recycling of aluminum cans. Please note that the conclusion compares % decline with decline in total weight. The total decline in weight of aluminum cans has to be more than the total decline in weight of plastic bottles. But if the % of decline in plastic is more , the decline could be because the sample space of plastic cans is smaller and the qty hence recycled is a greater % of this smaller qty.

POE :

a) This options conveys that the sample space of plastic is small because of a higher qty of glass bottles - hold
b) Are we concerned about the weight of plastic vs aluminum cans ? - out
c) We are not concerned about the fraction of beverage cans among plastic or glass bottles - out
d) How does the frequency of purchase matter ? Moreover we still cannot deduce that the sample space of plastic is smaller - out
e) Are we concerned with the number or weight ? - Out

Only option A seems feasible.

PurviGupta1998 · Answer

If the plastic cans are heavier than the aluminium cans, doesn't that signify the fact that even when recycling of aluminium cans was more widely practiced that recycling of of plastic cans, the smaller percentage of plastic cans being recycled accounted for the greater reduction in the weight? How does the fact that everything in the question is in percentages lead to us eliminating option B as an option choice?

Ashokshiva · Answer

Yes,I too agree with option -B

Say for example,weight of one plastic bottle =2kg

Weight of one aluminum bottle/can =1 kg

Since aluminum recycling is more popular,let us assume more aluminum cans are reduced from garbage.

If 150 aluminum cans are reduced and 100 plastic cans are reduced from garbage then weight of aluminum reduced would be 150kg,whereas weight of plastic reduced would be 200kg (100*2)

Kindly help us out  VeritasKarishma  &  GMATNinja

Thanks

KarishmaB · Answer

As I explained in my solution above, we do not know how popularity is measured. What do you mean when you say:
"Aluminium recycling was more widely practiced than plastic recycling."

Case 1: Does it mean that for every 10 Alu cans sold, 6 come back for recycling while for every 10 plastic bottles, only 4 come back?
Case 2: Or does it mean for every 10 kg of Alu sold, 6 kg comes back while for every 10 kg of plastic sold, only 4 kg comes back?

In any case, more Alu is getting recycled so less is going into the garbage.

But we do know that in 1000 kg of garbage, where we used to have 50 kg of Alu before, we now have only 40 kg but 50 kg of plastic has come down to 20 kg of plastic.

How come, in the garbage, the percentage of plastic is has reduced even more than the percentage of Alu? Perhaps because less plastic is being used nowadays. So though people are not very keen on recycling it (not as much as recycling alu), they are anyway using very less of it so little is going to find its way in the trash. Hence (A) is correct.

In (B), we do not know how we measure "Aluminium recycling was more widely practiced than plastic recycling."
If it is case 1, then it is possible that difference in weight of every unit accounts for the greater reduction in plastic weight. If it is case 2, then the greater reduction in plastic weight is not explained. Hence, this is not a good explanation of the discrepancy.

GMATNinja · Answer

Karishma covered this nicely as always, but I'll toss in my two cents again in case it helps somebody to hear the same ideas in a different voice.

We are not concerned with the TOTAL reduction (kg) of plastic or aluminum. We are concerned with  percent  decrease within each group (aluminum and plastic).

Let's say we start with 1000 aluminum cans and 1000 plastic bottles. Using the numbers in your example, we decrease by 150 aluminum cans and 100 plastic bottles. So aluminum goes from 1000kg to 850kg (15% reduction in weight). Plastic goes from 2000kg to 1800kg (10% reduction in weight). So the weight of the aluminum declines by a greater percentage in that case.

Remember, we are trying to explain why, "the total weight of plastic bottles in Brazil’s domestic garbage  declined by a greater percentage  during this time than the total weight of aluminum cans in Brazil’s domestic garbage."

I hope that helps!

NeoNguyen1989 · Answer

I'm not very convinced with the explanation of GMATNinja. The explanation  uses the assumption that   the number of the plastic beverage bottles used by Brazilians are equivalent with the weight of plastic in garbage " that would reduce the number of plastic beverage bottles used by Brazilians and thus reduce the weight of plastic in Brazil's garbage "

This assumption is the same with the assumption that is implied in the answer choice E which mention about the number of plastic bottles. E implies that since the number of bottles is lower for plastics than for aluminium, the weight of plastic bottles is also lower. Hence, it's might happen that % of decrease of plastics is higher but the absolute decrease of weight of plastics is lower than aluminium.

If both use the same assumption, why would A be correct and E would be incorrect?

GMATNinja · Answer

It’s important to remember the “apparent discrepancy” that we’re trying to explain. As we said in our previous post, the discrepancy is that while aluminum recycling was more widely practiced than plastic recycling from 2000-2010, “the total weight of plastic bottles in Brazil’s domestic garbage declined by a greater  percentage  during this time than the total weight of aluminum cans in Brazil’s domestic garbage."

So, the discrepancy is NOT related to the absolute weight of either plastic or aluminum. In fact, the passage gives us no information on the absolute weight of these two materials. Rather, the discrepancy is concerned with why the total weight of plastic recycled declines by a greater  percentage  than the total weight of aluminum recycled.

(E) gives us no information to explain that discrepancy, nor does it give any information regarding how things changed over the course of the decade. Therefore, we can eliminate it.

On the other hand, (A) simply requires that we assume that the number of plastic bottles recycled roughly correlates with the weight of plastic bottles recycled. In the absence of information to the contrary, this is a totally reasonable assumption. For that reason, (A) is correct.

I hope that helps!

SuyashSri · Answer

Understood the answers provided by  GMATNinja  and  VeritasKarishma 
my query is more conceptual. As mentioned in the explanation by GMATNinja, At first glance, this might seem to be out of scope, since the passage doesn't mention glass at all, i rejected Option A citing it's out of scope of the passage. So my query here is for all such CR questions should we not restrict the thoughts to what is clearly mentioned in the passage or anything under the Sun can be considered as a reason?

KarishmaB · Answer

Yes, option (A) mentions 'glass' but note that it mentions 'plastic' too and that is relevant. It tells you that plastic is increasingly being replaced by glass. This implies that consumption of plastic is reducing. What exactly it is being replaced by, whether glass or wood or something else is of course irrelevant to our argument. 
Also, strengthen/weaken/explain the paradox questions need new information from the correct option. So the correct option may have things that are not mentioned in the passage but are relevant to some aspect that is mentioned.

mSKR · Answer

During my practice with GMAT OG CRs, I realized that as far as option has some impact with the conclusion, irrespective of whether it is given in the argument or anything under the sun, we need to give thought to accept or reject the option.
When I read A.
(A) Consumers increasingly favored glass beverage containers over plastic ones.

I didn't focus on glass beverage containers but my eyes focused on plastic ones. I asked a question can there be some relation with the conclusion. I was not clear in 1st reading but I got one point that somehow plastic is getting reduced because of external factor. I kept on hold.
Another doubt came in mind: Is this information between the said period or could it be before 2000 ? Then I noticed the word " increasingly" . It seems recently something is reducing plastic. 
I kept on hold in my first reading . I was not sure of this answer. But after reading other options and rejecting other shortlist options , I could not argue more to reject A.

pk6969 · Answer

HI, In your example, if we take weight of aluminium cans garbage and plastic cans garbage before recycling as 1000kgs each. Now suppose aluminium cans weigh 1kg and plastic cans weigh 50kgs. Now after recycling, we were able to reduce 100 cans , so total weight of aluminium cans garbage will become 900kgs (10% reduction). For plastic cans, the number reduced by 10 cans, so total weight of plastic cans will now become 500kg (50% reduction in weight). Hence, it helps explain the discrepancy. Can you tell me where I am going wrong? I know this is an unofficial question and I took this question with a grain of salt.

GMATNinja · Answer

As you point out in your example, there are instances in which (B) could help explain the discrepancy. But as we point out in our example, there are instances in which (B) would not help explain the discrepancy.

Each of these cases are equally likely, so (B) really does little to explain the discrepancy. For that reason, we can eliminate it.

I hope that helps!

Rickooreo · Answer

In above question, OA is option A. I had marked B while solving. I understand that it is possible that the weight of B won't be sufficiently higher than A to offset the impact of the reduction in the quantity of waste generated. i.e % diff in weight of aluminium and plastic is 10% but reduction in waste generated is 20% then it is possible that % reduction in aluminum waste is higher than plastic even though weight is higher. Is this understanding correct

However, won't the same kind of logic be applied to option AEarlier weight of aluminum is 100kg, recycled 20 kgs thus reduction is 20%Earlier weight of plastic is 100 kg, recycled is 5 kgs and replaced with glass is 8kgs thus left is 87kg which is 13% reduction, thus A does not account for discrepany.

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