Parallel Reasoning Question

[siddus]

Most people who shop for groceries no more than
three times a month buy prepared frozen dinners
regularly. In Hallstown most people shop for
groceries no more than three times a month.
Therefore, in Hallstown most people buy prepared
frozen dinners regularly.

Which one of the following arguments has a flawed
pattern of reasoning most like the flawed reasoning
in the argument above?

(A) It is clear that most drivers in West Ansland are
safe drivers since there are very few driving
accidents in West Ansland and most
accidents there are not serious.

(B) It is clear that John cannot drive, since he does
not own a car and no one in his family who
does not own a car can drive.

(C) It is clear that Fernando's friends usually drive
to school, since all of his friends can drive
and all of his friends go to school.

(D) It is clear that most people in Highland County
drive sedans, since most people who
commute to work drive sedans and most
people in Highland County commute to
work.

(E) It is clear that most of Janine's friends are good
drivers, since she accepts rides only from
good drivers and she accepts rides from most
of her friends.


Answer Option: D

Source: LSAT CR Bible

Can someone point out to me the flaw in the argument stated above?

Thanks.

[grockit_andrea]

On a standardized test, "most" is assumed to have a specific meaning: at least 51%. Therefore, if MOST people in Hallstown grocery shop no more than 3 times per month, all we know is that at least 51% of people in Hallstown grocery shop no more than 3 times per months. Then, of that 51%, MOST buy prepared frozen meals; from that statement, all we know is that at least 51% of the people who grocery shop 3 times per month buy frozen meals. 51% of 51% is just over 25%, which would not be sufficient to be MOST of the people in Hallstown. Basically, the argument draws a strong conclusion that isn't adequately supported by the evidence, which only discusses statistics in terms of "most." In the correct answer here, the conclusion is stated in the first sentence instead of the last, but if you move it around so that the structure is the same as that of the original argument, you can see the parallels.

[siddus]

Thank you, that was very good.

An alternate explanation provided by the LSAT bible is that the statement is a general statement about a particular nation or state. Hallstown is a part of this larger entity hence it may or may not be possible that it inherits the specific attributes.

What are your views on this explanation?

[grockit_andrea]

I think the LSAT Bible explanation is basically addressing the same issue I did: the percentages that play out in a large sample don't necessarily translate in the same way to a smaller group. In my view, that's because the smaller group has to be further sub-divided to conform to the characteristics of the large sample, and we can't do that with much accuracy, since the word "most" doesn't give us a precise percentage. But I believe it's the same principle.