From 1978 to 1988, beverage containers accounted for a steadily decrea

The question asks us to "account for a finding," so let's take a look at the exact "finding" in the passage:

There is a discrepancy between this finding and the fact that "aluminum recycling was more widely practiced than glass recycling." This fact would otherwise lead us to expect the weight of aluminum cans in the trash to decrease by a greater percentage than that of glass bottles, because cans that are recycled would not end up in the trash.

Our task is to find an answer choice that explains the discrepancy between the finding and the evidence. Let's go through the answer choices:


The finding in the passage deals with change in the percentage of weight of both items. Even if glass bottles are heavier than aluminum cans, you would still expect their weights to be reduced proportionally -- so if aluminum cans are recycled more, you would expect the weight of aluminum cans in the trash to decline more by percentage than the weight of glass bottles.

Answer choice (A) would be relevant in studying the change in total weight of these materials, but not so much for percent of weight. This factor does not explain the discrepancy in the change of percentage of weight. Answer (A) is out.


If you look back at the "finding" in the passage, it does not mention beverage containers at all. We are concerned only with the weight of glass bottles and aluminum cans in the trash by percentage. The contents of those glass and aluminum objects are irrelevant to the conclusion, so answer (B) is out.


This is more like it. We need a reason for a greater decline in percentage of glass bottles in the trash than aluminum cans in the trash, and answer (C) gives us a good reason. Households replaced "many" glass bottles with plastic containers, while only replacing "few" aluminum cans with plastic. So fewer glass bottles would end up in the trash despite more aluminum cans being recycled. This accounts for the discrepancy between the evidence and finding.

(C) is looking great, but let's finish up the other answer choices.


We are looking for a reason that the percentage of weight of glass is lower than expected when compared to that of aluminum. Answer (D) states that household purchases of glass bottles is increasing faster than purchases of aluminum. This is the opposite of what we need to resolve the discrepancy, so answer (D) is out.


This answer might explain why aluminum recycling is more widespread than glass recycling, but it has nothing to do with the central discrepancy we are trying to resolve: why did the percentage of weight of glass decrease more than that of aluminum?

Answer (E) is out, and answer (C) is correct.
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The answer is C.

The question asks "what catalyst aside from recycling could cause the overall weight of glass garbage to decrease?"

A. The actual weight of glass is irrelevant as it has remained the same through time.

B. Who cares what was in the glass, as the weight is not effective.

C. Bingo! There is less glass being circulated, therefore the aggregate weight of glass will be less.

D. should have the opposite effect.
E. Color sorting, however interesting, is outside of the scope of this question

C.
you have to find some other factors that cause glass weight to be less than aluminum. C fits this.

This one is a bit tricky.

B: Irrelevant.
D: I think this suggests that the overal % should be greater.
E: Irrelevant.

Btwn A and C I was stuck. I chose C simply b/c I didn't feel right w/ A. I couldn't put my finger on it, but I felt that A was missing something crucial here.

Can someone please explain further why A is wrong?

I think C is not the right answer, because in C it says that glass bottles are replaced by Plastic containers, it no where mentions the weight of the plastic containers, it might be possible that plastic containers are heavier than small size bottles.

Paradox: glass decreased (%) more than aluminum did (%) even when recycling aluminum was more common.
You say the plastic containers can be heavier than glass bottles. That's fine. Plastic can be 1000 tons greater than glass. Still, the glass was replaced by plastic, and the paradox only requires explanation how glass decreased (%) more than aluminum (%).

I hope this helps.

I guess only contention is between Option A) and Option C) - OA is Option C)

Let me explain why Option A) is wrong (BTW : I marked option A in the Mock )

There is decline in the weight of the garbage and majority of the decline is weight is contributed by the recycling process.

Aluminium recycling > Glass recycling.

But decline in weight of aluminium bottles is less than decline in the weight of glass bottles. The question doesn't say that the relative decline of aluminium bottles is less than relative decline of glass bottles

Lets say 100Kgs of garbage

Now earlier out of 100 kgs, 30 kgs was contributed by AL bottles and 10 kgs (lets say) is contributed by GL bottles.
Lets say AL is heavier and is 1 Kg and GL bottles is 0.5 kg
So contribution for AL was 30% and for GL bottles it was 10%

Now lets say 10 AL bottles are recycled and lets say 8 bottles
So the weight of AL bottles decreases by 10 Kgs
and for GL it is 4 kgs.

So decline by weight of AL = 10/30 = 33.33%
And decline by weight of GL = 4/10 = 40%

Even though the recycle of AL bottles is more than recycle of GL bottles, the decline in the weight of GL as a % > decline in the weight of AL as a %.

C) is correct as denominator is changed by Manufacturers and hence it explains the paradox.
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(c) Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.
=> Weight of glass bottles in household garbage declined by a greater percentage than the weight of aluminum cans.
Percent Change = new-old/original, I mean, you calculate the change of one material compared to its original weight, and not the weight of the other material !

Aluminum canns 100 units -> recycled 50 and replaced with plastic 10 -> 40 units left over ----> Decrease 60%
Glass Bottles 100 units -> recycled 30 and replaced 50 with plastic -> 20 units left over ----> Decrease 80%

Also got trapped by A.....

From 1978 to 1988, beverage containers accounted for a steadily decreasing % of the total weight of household garbage in the United States. The increasingly widespread recycling of aluminum and glass was responsible for most of this decline. However, although aluminum recycling was more widely practiced than glass recycling, it was found that the weight of glass bottles in household garbage declined by a greater % than the weight of the 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.
This shouldn't matter. We are talking about the % decline over a period of time, not the overall weight.

(b) Recycled aluminum cans were almost all beverage containers, but a significant fraction of the recycled glass bottles had contained products other than beverages.
This also shouldn't matter. Who cares what is inside the recycled glass bottles--the bottles are in the trash, so the contents of what was in them should be emptied or somewhere else. The conclusion is about the bottles in the trash, not the bottles before they enter the trash. Even if it were true, what's inside the glass bottles could be heavier or lighter than the aluminum cans.

(c) Manufacturers replaced many glass bottles, but few aluminum cans, with plastic containers.
This is our answer. If manufacturers replaced the glass bottles with plastic, as a %, the weight of the glass bottles compared to everything else would go down. Since this says aluminum cans were replaced fewer than glass bottles, the conclusion makes logical sense.

(d) The total weight of glass bottles purchased by households increased at a slightly faster rate than the total weight of aluminum cans.
If this were true, it would mean the conclusion of the stimulus should be exactly the opposite.

(e) In many areas, glass bottles had to be sorted by color of the glass before being recycled, whereas the aluminum cans required no sorting.
This has nothing to do with the weight.

IMO C
Explanation for answer choices:
a) Comparing the weight of the glass bottles and aluminum cans would not tell anything why the weight of the glass bottles declined in the garbage.
b) Even if the cans and bottles contained other products it is irrelevant in this scenario.
c) Because many glass bottles were replaced but fewer aluminum cans with plastic containers, and as the glass bottles weigh more reduction in the usage directly affects the weight.
d) Increase in the weight does not say anything for the de[/color]cline
e) Sorting the glass bottles does not change anything.

GMATNinja

Please help in deciphering the argument and correct choice!

As per the statement it says most of "the decline of total % weight of beverage" is attributrf to recyclable aluminium and glass.

The aluminums were more recycled and glasses were not.

As per the logic, can't we deduce that the recycled glass was not returned back to the cycle?

I mean what if the glasses were used for other purposes on recycling. And option B fits properly for that.

I agree that c is right but why b is wrong ? Considering the above fact?

Posted from my mobile device

Hi Rish2708,

I think that your thinking is good, but I believe that you've misinterpreted B in some way. The passage talks about GALSS BOTTLES, so even if they contained something else, they were still brought to the cycle because they are the same recyclable objects.

Hope this helps

Hi! Can you explain why you say "it does not mention beverage containers at all"

The passage seems be specifically about"beverage containers". It says:

beverage containers accounted for a steadily decreasing % of the total weight of household garbage in the United States.

I was emphasizing that the finding (the weight of glass bottles in household garbage declined by a greater % than the weight of aluminum cans) doesn't mention whether or not the bottles and cans contained beverages.

We eliminate (B) because the contents that these bottles and cans previously contained is irrelevant to explaining the discrepancy in % weight decrease of the bottles and the cans themselves.

I hope that helps!
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GMATNinja VeritasKarishma

I am always confused when the questions include percentages.

"it was found that the weight of glass bottles in household garbage declined by a greater % than the weight of the aluminum cans. "

How do I express this mathematically? Always confused about what to take the base as.

Is it (weight of glass bottles decreased)/total weight of garbage? (weight of glass bottles decreased)/ (total weight of glass bottles)

Always get stumped when they mention a percentage because I have difficulty in finding the base.

Weight of glass bottles declined by a greater percentage than the weight of aluminium cans.

Say weight of glass bottles was 100 tonnes in garbage.
It has declined to 80 tonnes i.e. a percentage reduction of 20/100 = 20% reduction in weight

Say weight of aluminium was 300 tonnes too.
If has declined to 270 tonnes i.e. a percentage reduction of 30/300 = 10% reduction in weight

So weight of glass bottles has seen a higher reduction in weight.

When we say A has increased/decreased by 10%, we are talking about the new value of A compared with the OLD value of A itself.
A number increased by 10% means now the number is 10% more than its previous value. So if the number were 50, it is now 55.

Posted from my mobile device
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This is find the discrepancy type question.

Although B is a slight contender. it is ruled out because of beverage container blah blah stuff.

Only C fits in by giving the right reason for the decrease in the weight of glass bottles

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

- Largely because of the widespread recycling of aluminum and glass, beverage containers accounted for decreasing % of total weight of garbage
- Aluminum recycling more widely practiced than glass recycling but weight of glass bottles in household garbage declined by a greater %.

If aluminum recycling was more widely practiced than glass recycling, one would expect that the weight of aluminum in household garbage declined by a greater %. Instead, we’re told the weight of glass bottles in household garbage declined by a greater %. We need to find an answer choice that explains this finding.

A. Good to know. It’s completely irrelevant to the argument, though. This is the trap answer. You might think that since glass bottles are heavier than aluminum cans, this would explain why the weight of glass bottles declined by a greater %. But we’re comparing the percentage change of glass bottles (weight of glass bottles in household garbage in 1978 to the weight of glass bottles in household garbage in 1979)

B. Irrelevant distinction. We know they’re glass bottles – whether they contain beverages or something else is not important.

C. If manufacturers replaced many glass bottles with plastic containers, this would explain why aluminum recycling was more widespread and why glass bottles in household garbage declined by a greater %.

D. So the weight of glass bottles purchased by households increased at a slightly faster rate than total weight of aluminum cans. This is not important – we’re concerned with explaining why the weight of glass bottles in household garbage declined by a greater % than weight of the aluminum cans.

E. Irrelevant.

Answer is C.
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