need help urgently - MGMAT Verbal Question

[sudaif]

A recent study demonstrated that parents living with children consume nearly five more grams of fat per day, on average, than do adults living without children. The higher fat intake among these parents is probably attributable to their snacking on the pizza and cookies that tend to be plentiful in households with children.

Which of the following, if true, would most seriously weaken this explanation of the parents' higher fat intake?


On average, households with children spend $15 more per week on pizza and cookies than do households without children.
Households with children purchase much more whole milk, which has a high fat content, than do households without children.
Children consume most of the pizza and cookies in any given household.

Parents ought to set a good example for their children, in dietary choices as in other matters.
Not all parents living with children consume more grams of fat than do adults living without children.

-------the answer that MGMAt points out is B.
Here is my problem with it.
Isn't the argument based on the fact that parents who live in households with children are the ones consuming more fat than those living without children? If so, the source of the fat is important but having the children in the house is more important, no? If you agree, then if the children eat most of the snacks and pizza --- leaving little for the parents---then parents will be unable to consume as much pizza and snacks. In short, isn't answer C the correct answer?

[mschwrtz]

If an argument contains two claims X and Y, such that X explains Y, then Y is the evidence and X the conclusion. If you're asked to weaken such an argument, there's a pretty good chance the right answer will suggest an alternative explanation for the evidence. Here, the question stem suggest that you want a counter-explanation.

The argument runs,

...parents living with children consume... fat per day....

THEREFORE

...these parents... probably... snack on... pizza and cookies ....

Answer choice B gives an alternative explanation for the extra fat. C isn't a bad answer, it really does weaken the conclusion, but it's not as good as B. Part of the problem with B is that even if children consume most of the pizza and cookies, parents in such households might well consume more than adults in other households; 10% of all the extra fat is still more fat. Also, B is not the sort of answer most likely to be correct for a question with this sort of structure and question stem.

Incidentally, often the item-writer will help you out, and use the word "must" to signal the conclusion. Less often she'll help you out and use the word "only."

Where the question at hand reads "The higher fat intake... is probably attributable to their snacking...," we might have had "The higher fat intake... must be attributable to their snacking...," or "The higher fat intake... could only be attributable to their snacking...."

Even though the item-writer didn't use a tip-off such as "must," she did write right there in the question that the conclusion was an explanation. Another reason to read the question first.

[koolk86]

Households with children purchase much more whole milk, which has a high fat content, than do households without children.

I have a question here. The above statement says " household purchase more milk" BUT purchase and actual consumption might be by different people. So is there an underlying assumption here that since they have purchased they are the ones who will consume ?

If yes, when can we assume such things?

Thanks in advance.

[StaceyKoprince]

The text you've reproduced above is one of the answer choices. We're asked to pretend, essentially, that each of the answer choices is true - but only as far as it goes. We don't make any assumptions about what else the choice might be implying - we just take what it says at face value. But what we're trying to do here is more complicated than this.

Our task here is to find a choice that weakens "this explanation of the parents' higher fat intake?"

What is "this explanation of the parents' higher fat intake?"

according to the argument, this "is probably attributable to their snacking on the pizza and cookies"

So we're trying to weaken the idea that parents consume more fat because they snack on pizza and cookies. Not just that they consume more fat.

Weakening such a line of reasoning simply means introducing information that would lower the likelihood that the original line of reasoning is valid. We don't have to completely negate the line of reasoning or "prove" that the conclusion is incorrect.

So, I claim that parents have higher fat intake because they're eating pizza and cookies. You point out that households with kids also tend to buy more whole milk, which has a higher fat content than regular milk.

Have you just introduced a new piece of information that casts doubt on my line of reasoning? Sure. It's possible that parents are drinking more whole milk than non-parent adults. We don't have to assume anything in order to say that this is possible - we don't have to assume that it must be true. It's just possible, and that's enough to say, "Well, Stacey, your pizza and cookies theory isn't looking as good as it used to before we knew about this milk data."

[sudaif]

Thanks Mschrtz and Stacey. This was v helpful.
I had one follow-up question...i've noticed that almost all CR questions that involve strengthening/weakening can be reduced to simple or complex causality arguments? is that the right way to approach them then? Thanks.

[mschwrtz]

I think that that might be a bit strong, sudaif. But keep alert to that possibility.

[RomanR561]

If an argument contains two claims X and Y, such that X explains Y, then Y is the evidence and X the conclusion. If you're asked to weaken such an argument, there's a pretty good chance the right answer will suggest an alternative explanation for the evidence. Here, the question stem suggest that you want a counter-explanation.

The argument runs,

...parents living with children consume... fat per day....

THEREFORE

...these parents... probably... snack on... pizza and cookies ....

Answer choice B gives an alternative explanation for the extra fat. C isn't a bad answer, it really does weaken the conclusion, but it's not as good as B. Part of the problem with B is that even if children consume most of the pizza and cookies, parents in such households might well consume more than adults in other households; 10% of all the extra fat is still more fat. Also, B is not the sort of answer most likely to be correct for a question with this sort of structure and question stem.

Incidentally, often the item-writer will help you out, and use the word "must" to signal the conclusion. Less often she'll help you out and use the word "only."

Where the question at hand reads "The higher fat intake... is probably attributable to their snacking...," we might have had "The higher fat intake... must be attributable to their snacking...," or "The higher fat intake... could only be attributable to their snacking...."

Even though the item-writer didn't use a tip-off such as "must," she did write right there in the question that the conclusion was an explanation. Another reason to read the question first.

Following your logic it is not clear whether parents drink that milk; answer stated only about purchasing, which is clearly not the same as consuming.