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This isn’t really relevant as written. It could’ve been relevant if it said that during that specific period the weight of plastic bottles has changed. However it does not say that and we’re assuming that the weight of the plastic bottles was constant during before and after the period of observation.

Hope it helps.


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Hello,

Could you please elaborate on why B is wrong? Wouldn´t heavier plastic bottles mean that, even if there is less recycling of plastic, there could be a greater decline of total waste weight because of the weight of the plastic bottles?

Posted from my mobile device
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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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MartyMurray & GMATNinja - Please help explain how to eliminated b/w A&B
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Taking some chatgpt help:
Statement B (heavier plastic)

What B is saying in maths

Plastic units weigh more than aluminum units.

Example

One plastic bottle = 2 kg

One aluminum can = 1 kg

Garbage before → after:

Plastic: 100 kg → 60 kg
% drop =
40
100
=
40
%
100
40


=40%

Aluminum: 50 kg → 30 kg
% drop =
20
50
=
40
%
50
20


=40%

👉 Heavier weight does NOT change % drop

So B cannot explain why plastic % drop is bigger.

total weight "of plastic bottles" in Brazil’s domestic garbage - base is not same for both

This is the key misunderstanding, so let’s fix it cleanly.

👉 The base is NOT the same for plastic and aluminum.
Each % is calculated on its own base.
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Can someone explain why (B) and (D) is wrong in easier terms?
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Can someone explain why (B) and (D) is wrong in easier terms?
Why B is incorrect?
The passage talks about "percentage" of decline,
If initial weight was 100kg and 10kg for plastic and aluminium respectively, and both were recycled, decline is 50% for both
B says plastic is heavier, that doesn't mean rate of removal was faster for plastic, it just means initial weight was more.
If plastic is heavier and harder to recycle you would expect it to be more in the garbage and not less.

Why D is incorrect?
If people buying more plastic than aluminium, it doesn't resolve the paradox, it worsens it. If people are buying more plastic AND plastic is recycled less often, there should be a mountain of plastic in the trash. This makes it even more confusing why the weight of plastic in the garbage went down. Choice D "strengthens" the paradox instead of solving it.

A however directly addresses the issue, if people favored glass over plastic, plastic is bound to decrease.

Hope it helps!!
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This is a great question that’s helpful for learning and I like the solution - it’s helpful.
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Why Option B is wrong:

In 2000, there were 100 aluminium cans, weighing 10 kg each, and 100 plastic bottles, weighing 20 kg each.

100 aluminum cans × 10 kg = 1,000 kg
100 plastic bottles × 20 kg = 2,000 kg

In 2010, the number of aluminium cans reduced to 90, and the number of plastic bottles reduced to 91 (aluminium decreased more than plastic, as the question suggests).

90 aluminum cans × 10 kg = 900 kg
91 plastic bottles × 20 kg = 1,820 kg

Percentage decline:

Aluminium: (1,000 − 900) / 1,000 = 10%
Plastic: (2,000 − 1,820) / 2,000 = 9%

Notice something interesting:

The percentage decline in weight is the same as the percentage decline in the number of containers, because the weight per container is constant.

Why?


(100×20)−(91×20) 100-91
------------------------- = ---------
100×20 100


=9%


The 20 kg cancels out.

Percentage decline in total weight = Percentage decline in the number of items.
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This is a great question that’s helpful for learning and I don’t quite agree with the solution. A explains why plastic bottle waste decreased (people switched to glass), but it doesn't directly explain why plastic declined by a greater percentage than aluminum.
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This is a great question that’s helpful for learning and I don’t quite agree with the solution. A explains why plastic bottle waste decreased (people switched to glass), but it doesn't directly explain why plastic declined by a greater percentage than aluminum.


You’re right that A) does not guarantee a greater percentage decline. The trick is that the question asks what “most helps” explain it.

And A) introduces a second reason for plastic waste to fall - consumers used fewer plastic bottles but it does not give a similar reason for Aluminum, so that is the reason why Aluminum remained unchanged so to speak.
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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.

This is an old comment and I see someone gave it Kudos so perhaps also has the same question - let me explain a bit more.

1. The difference of the weights of materials may seem important at first but it does not matter how much 1 plastic bottle or 1 can weights because we are looking at total numbers year over year. So we are looking at trends and changes, not absolute numbers or individual weights. Yes, one may be super light or another is super heavy but they would have been super light or super heavy a year ago and they will be next year unless a new technology arrived which we are NOT told anything about, so any answer choice that picks on individual contains will not hold up the logic test. I hope this is clear. This is what Eliminates B).

2. In your particular calculation we are supposed to look year over year. I think you did not setup the numbers correctly. It should be like this:

Last Year:
Total: 100kg of plastics
Recycled: 5kg
Garbage: 95kg

This year:
Total: 90kg of plastics
Recycled: 4kg
Garbage: 86kg

So there is a decrease from 95kg to 86kg in this case

For Option A - the calculation is much simpler and there is none to have really. Recycling is not responsible for the change and rather it is the decline in the total plastics garbage product mix. Some of the plastics is replaced with glass and thus the total input of plastic which was going partially to garbage and partially to recycling is now less and so naturally it would decline.

I hope it helps. You do not need any numbers, though you are welcome to apply them if you think it helps.
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