GMAC Practice Test: Critical Reasoning

[jp.jprasanna]

As this question has appeared in GMAT prep as well, I hope this question can be discussed.

Full questions below - OA B NOT A

A recent report determined that although only 3 percent of drivers on Maryland highways equipped their vehicles with radar detectors, 33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them. Clearly, drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are driver who do not.

The conclusion drawn above depends on which of the following assumptions:

(A) Drivers who equip their vehicles with radar detectors are less likely to be ticketed for exceeding the speed limit than are drivers who do not.
(B) Drivers who are ticketed for exceeding the speed limit are more likely to exceed the speed limit regularly than are drivers who are not ticketed.
(C) The number of vehicles that were ticketed for exceeding the speed limit was greater than number of vehicles that were equipped with radar detectors.
(D) Many of the vehicles that were ticketed for exceeding the speed limit were ticketed more than once in the time period covered by the report.
(E) Drivers on Maryland highways exceeded the speed limit more often than did drivers on other state highways not covered in the report.


My doubts :

Premise supporting this conclusion is that "3% of the vehicles equipped with Radar accounts for 33% of the vehicles(with radar)ticketed for over speeding"

so these drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are driver who do not.

So for ONLY this 3 % to account for 33% then they must hve been ticked more than once (option D ; otherwise how would 3% account for 33%) and also these Drivers, who are ticketed for exceeding the speed limit, are likely to speed over and over again (option B otherwise how would 3% account for 33%).

Is my above understanding correct?

Also My guess is since the author is making a projection "drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are driver who do not. " And Since we are asked pick an assumption - Option B looks more fit.

If We asked to justify the conclusion or resolve the paradox Option D would have been the right answer
- Is this reasoning correct or Am i off mark again?

I'm really not sure how A can be correct as posted by the user in 2007!

[RonPurewal]

i went ahead and killed the earlier posts, since they referenced an incorrect answer as "correct".

basically, the only real hole in the argument is that it presents evidence about people who receive speeding tickets, but then goes on to draw a conclusion about people who speed regularly.
for this argument to work, the first group -- people who actually receive tickets -- must actually be representative of the second group (regular speeders).
that's what is established by the correct answer.

--

analogy:
people with mental disorder X are convicted of crime Y at ten times the rate observed in the general population. therefore, people with mental disorder X are more likely than other people to commit crime Y.

--> this argument doesn't work unless you establish that the group of people convicted of the crime actually constitute a representative sample of everyone who commits it. (this doesn't have to be true; for instance, it's possible that people with and without mental disorder X commit the crime at equal rates, but that people with the mental disorder simply behave in a way that allows them to get caught more often.)