GMAT CLUB OLYMPICS: Local authorities claim that following a recent re

My answer is (C).

Pre-thinking
Why 1% instead of 0.1%? This question seems to require some outside knowledge. If 0.1% can cause significant cognitive impairment, this measure cannot greatly reduce car accidents. On the other hand, if people's blood alcohol concentration is normally at 1.1% or higher, local authorities will be driven out of office by locals.

The only consequence of being caught with 1% or higher is to have driving license revoked, rather than to imprison the one-percenter for the rest of their lives. What if people are all willing to drive without license?

The measure only apples to drivers caught with 1%. What if only 1% of offenders can be caught?

Now, take a look at options:
(A) This deterrence scenario can reasonably occur. But the argument does not reply on it. The argument focuses on removing drunk drivers.
Still, I would keep it for now.

(B) What is the precise meaning of "greatly" in "greatly reduce the number of car accidents per year"? If by "greatly", the local authorities tries to cut car accidents by 99%, it does has dependency on this fact. On the other hand, if 5% reduction is already considered "greatly", whether this statement hold does not hold.

(C) The best answer. If has to be true for the authorities plan to work. It directly defeats the only consequence of being found with violation. If license revocation cannot prevent people from driving and causing the majority of car accidents, implementing such measurement may not reduce car accidents "greatly".
Certainly, some people won't drive without license. This measure can still reduce car accident incidence, if only by merely reducing the number of drivers on the road. Some politicians will still call it a great success.

In test center, I would choose (C) and go to the next question. I think no other answers can beat (C).

(D) it turns out to be a strong contender. 1% can be an arbitrary number. If the reality is:
> Drivers who have 0.1% - 1% blood alcohol are most likely to cause accidents.
> Drivers who have 1%-2% blood alcohol are 90% less likely to cause accidents. (Most of them are too drunk to start the car.)
> Drivers who have 2% or higher blood alcohol cannot even walk to their cars and thus would not cause any car accidents.
Still, (D) does not mention driver license, which is the core to the local authorities' legislation.

(E) This one explains why 1% is a reasonable threshold.
But the measure does not depend on it. Once drivers hit 1% or higher, maybe their reaction times shorten, which can also cause accidents.
Again, (E) does not mention driver license.

Local authorities claim that following a recent report showing that the chance that a driver is involved in a car accident increases with that driver’s blood alcohol levels, they have decided to legislate the following law, which they expect to greatly reduce the number of car accidents per year: “Drivers caught with a blood alcohol concentration of 1% or more will have their driving license revoked.”

Which of the following does the local authorities’ argument rely upon?

A. The threat of a revoked license causes drivers to drink less alcohol before they drive, reducing the total number of car accidents. we need to eliminate drinking altogether not just the amount they drink

B. The majority of drivers who cause accidents usually drive with 1% blood alcohol or more. irrelevant

C. The majority of car accidents are not caused by drivers who drive without a license. necesssary assumption.if negated tores the argument

D. When driving, drivers who have less than 1% blood alcohol are statistically unlikely to cause accidents. this strengthening but not a necessary assumption

E. Once drivers’ blood alcohol concentration rises above 1%, their reaction times slow, making them unable to respond in time to dangerous situations. This is not a necessary assumption

Dear IanStewart


Your help in sorting out this problem would be invaluable.
I don’t like any of the answer choices. The correct choice must be a “required” assumption

The stem says that “the chance that a driver is INVOLVED in a car accident increases with that driver’s blood alcohol levels”.
This excerpt doesn’t necessarily mean that alcohol consuming drivers actually “cause” the accident. They are simply involved. They may have caused it, or just were the part of an accident caused by someone else. Demographics may mostly consist of reckless driving youth and carefully driving old people with some beer inside, who may get into trouble because of multiple races these youth organize, and so on. There can be many scenarios in which alcohol consuming people are actually not the cause of the accident.

If the licenses of such old people are revoked then the number of accidents are not going decline significantly. We need an answer choice that shows these alcohol consuming people are ACTUALLY causing the accident. I think B gives us this link and a better option than C. However, B still doesn’t necessarily have to be true.


The negation of C says that 50% or more accidents are caused by the drivers without licenses. In such a case the conclusion may still hold true because the remaining accidents are still a considerable amount. And if these 49% or fewer accidents are caused by alcohol consuming people, then the number of accidents is still going to drop considerably. So, C isn’t our assumption.

This was my way of thought. It would be much informative to know your thoughts on this. Many thanks beforehand.

It's a bit of a ridiculous question, because someone with a blood-alcohol level of 1% will be dead, so it won't matter if you revoke their driver's license. They presumably mean 0.1%. The first sentence of the stem is also bizarre: "Local authorities claim... they have decided to legislate the following law". What is the word "claim" doing there? Is it possibly untrue that they will enact this law?

Anyway, to respond to Jon's points: I agree there's a potential correlation-causation error in the stem (maybe it's young drivers who are most often drunk drivers, and maybe young drivers are reckless drivers and cause a lot of accidents whether they drink or not, so even if the law works as a complete deterrent, it might have no effect), so that might be the assumption the right answer addresses.

But the argument relies on many other assumptions too, and we only need to find one of them. For example, the argument is also assuming people won't drive dramatically more often after the law is in place -- if driving increased a lot, you'd possibly have more accidents even if drivers were safer. Or more fundamentally, the argument is assuming some people right now in this locality drive with a blood-alcohol level at or near 1% (if no one does now, the law won't accomplish anything). And it's assuming there is a great number of accidents in the locality right now, because if there isn't a great number, it's hard to see how they could "greatly reduce the number". So an answer choice addressing any of these issues would have been correct.

The argument does assume that revoking licenses will have some effect on driving behaviour, or on drinking behaviour. If people are perfectly willing to drive without a license, and the law has no deterrent effect, then the law might not accomplish anything. So an answer something like C is a good answer here, though I have no idea what the phrase "the majority of car accidents" has to do with anything in C -- the argument isn't specifically relying on any particular fact about "the majority" of accidents. It's hard to evaluate answers A and B in this question, because we don't know enough about how the law will accomplish its objective, nor about driving behaviours in this location. If it's true in this place that everyone drives after drinking once in their lifetime only, then this law will only work if it has a deterrent effect -- revoking a person's license won't achieve anything if the person was never going to drive drunk again. If instead most people drive sober, and a few people drive drunk on a daily basis and cause accidents all the time, then revoking licenses will work by getting habitual accident-causers off the road. The argument is assuming the law will achieve one of those two objectives, but we can't easily tell which one, and answers resembling A and B could be right depending on how the law will work. Overall it's not a very precisely constructed question, so it's not easy to really say what answer is best, though I'd pick C if forced to choose.

I should add one last point about answer C, to explain why it's not a great answer as written: suppose C was false. Then we'd know that right now, before this law is passed, most accidents are caused by people without a license. So it's those license-less drivers who are the problem -- they're apparently very bad drivers. It's not clear what a law about drinking will do to make those license-less drivers drive more safely. If we wanted to dramatically reduce accidents, we'd want to get those license-less drivers off the road, presumably.

What we really want to know about is how drivers will behave in the future: are the drivers who currently *do* have a license going to be willing to drive without one if they get caught under the new law? Answer C doesn't address that at all, but that's what we need answer C to address if it's going to be a necessary assumption.

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