Q32 MGMAT CAT Studies have shown that an automobile

[saurabhbanerjeeiimk]

Q. Studies have shown that an automobile that runs on a blend of 85% ethanol/15% gasoline gets better mileage than an otherwise similar car equipped with a gasoline engine. Many American legislators have concluded that an increase in tax incentives for ethanol production would lessen our dependence on foreign oil.

A) It takes 1.5 gallons of oil to produce 1 gallon of ethanol.
B) Electric cars are cheaper to operate than cars running on the ethanol fuel mix.
C) It costs thousands of dollars to retrofit an automobile to run on the ethanol fuel mix.
D) The ethanol/gasoline blend emits more pollution that regular gasoline.
E) The ethanol/gasoline blend has not been widely adopted in Europe.

I rejected option "A" because it switches terms. However the explanation marks it as the right answer. Please advice

[tim]

you have not actually posted the question. please post the full text so we can help you..

[harsh.narsinghani]

Studies have shown that an automobile that runs on a blend of 85% ethanol/15% gasoline gets better mileage
than an otherwise similar car equipped with a gasoline engine. Many American legislators have concluded that an
increase in tax incentives for ethanol production would lessen our dependence on foreign oil.
Which of the following, if true, casts the most doubt upon the validity of the legislators’ conclusion?
- It takes 1.5 gallons of oil to produce 1 gallon of ethanol.
- Electric cars are cheaper to operate than cars running on the ethanol fuel mix.
- It costs thousands of dollars to retrofit an automobile to run on the ethanol fuel mix.
- The ethanol/gasoline blend emits more pollution that regular gasoline.
- The ethanol/gasoline blend has not been widely adopted in Europe

I have a doubt how is option A the correct answer here. What if the mileage increases two folds? Please advice!

[tim]

don't add extra assumptions to this sort of question. treat the question as though it said "all other things being equal..."

by your logic, you could erroneously eliminate all five answer choices on virtually every CR question, which is definitely not what you want to accomplish..

[harsh.narsinghani]

Hi Tim,

Thanks for the reply. The point I am trying to make is that the passage states the mileage would be better for automobiles running on ethanol/gasoline mixture than automobiles using gasoline engine. So, if the mileage increases by a factor of less than 1.5x then option A weakens the argument, but if the mileage increases by a factor greater than 1.5x then the conclusion still holds. Mileage increase by two folds was just an example.Please share your thoughts.

[tim]

i really don't wish to be rude, but there is nothing else to share. as i said before, you are adding assumptions where you shouldn't. you need to take exactly what is on the page and answer exactly the question the test asks. this is just how the GMAT works..

[saurabhbanerjeeiimk]

I rejected option "A" because it switches terms. However the explanation marks it as the right answer. Please advice

[RonPurewal]

I have a doubt how is option A the correct answer here. What if the mileage increases two folds? Please advice!

the best (and most accurate) response to this kind of thing is "weaken doesn't mean destroy". in other words, it's significant that the questions say "weaken" and "strengthen", rather than "destroy" and "confirm".
so, while you are correct that choice (a) does not completely destroy the argument, that's immaterial, because it doesn't have to destroy the argument.
however, it should be clear that, on balance, choice (a) works against the argument -- because, according to that choice, not only do we have to use oil to produce ethanol, but we actually have to use more than x units of oil to produce x units of alcohol.

in fact, even the fact that 1.5 > 1 isn't really relevant here; even if that number were 0.5 instead of 1, choice (a) would still weaken the argument.
see, in the original argument, the notion that oil is required to produce ethanol isn't even present -- i.e., the default assumption is that, to produce 1 gallon of ethanol, we need 0 gallons of oil. therefore, an answer choice suggesting that we need any oil whatsoever to produce ethanol will actually weaken the argument.

--

the other question that needs to be asked here -- a question that people seem to be avoiding altogether thus far -- is this: what other answer choice did you think was a contender?
even if you did have doubts about choice (a), that should all have gone away when you looked at the other answer choices, none of which has the least bit of relevance to the issue of oil consumption (which is the crux of the argument).

this is also an important principle: you're not looking for a perfect answer, you're just looking for an answer that's demonstrably better than the other four answers.