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
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