V21-06

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.

Bunuel · Accepted Answer

Official Solution:

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.

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.
 
(A) Consumers increasingly favored glass beverage containers over plastic ones.
 
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). 
 
(B) Plastic bottles were significantly heavier than aluminum cans of comparable size.
 
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.
 
(C) Most recycled aluminum cans were beverage containers, but a significant fraction of recycled plastic bottles were not beverage containers.
 
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.
 
(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.
 
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.
 
(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.
 
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.

Answer: A

gmatlc · Answer

Bunuel 
 jeffn

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?

bb · Answer

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.

Posted from my mobile device

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.

Goldenfuture · Answer

MartyMurray  &  GMATNinja  - Please help explain how to eliminated b/w A&B

Goldenfuture · Answer

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.

canopyinthecity · Answer

Can someone explain why (B) and (D) is wrong in easier terms?

bhanu29 · Answer

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!!

Sunny3897 · Answer

This is a great question that’s helpful for learning and I like the solution - it’s helpful.

Sunny3897 · Answer

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.

TrackPoint · Answer

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.

V21-06

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards