While my primary area of expertise is not writing GMAT questions, I would judge that this question is not realistic to the test.
This question is still good practice for a number of points for the right method for Critical Reasoning questions. Ask yourself whether you read the question stem first and identified the question type before moving on to the stimulus (step one of the proper method). Also, when you read the stimulus, you should have had three predictions as to what the answer was:
1) Since there is a causal argument, that’s very possibly the flaw. Causal arguments tend to overlook other possibilities – most dramatically, the possibility that something else was the cause of the phenomenon in question. I.e., the argument says A->B, but in reality, C->B.
2) Numbers vs. proportions. Arguments in CR questions frequently confuse or improperly mix measures of absolute numbers with measures of rates. We are told about the numbers of crimes, and the number of migrants, but since we don’t know the sizes of the populations, we don’t know anything yet about (for example) Abstania’s actual crime RATE. (The word “dramatically” slightly mitigates this error by implying that what’s being considered is actually a proportion, making the error a bit too subjective for a proper test question imho.)
3) Lastly, you can always use a more traditional approach for dissecting the argument and looking for a critical assumption.
Those are the things you should be thinking about before even looking at the answer choices.
A) neither weakens or strengthens the argument, because we don’t know the percentage apprehended, only the absolute numbers. Monrovia could be a lawless terror zone, with lots of unresolved crime. Or, law enforcement could be equally effective in both countries, in which case A) would imply that Monrovia has less crime than Abstania.
B) doesn’t tell us much either, because we don’t know the population of either Abstania or Monrovia. Abstania could be much much larger than Monrovia, in which case its crime rate would actually be low compared to Monrovia’s, or something more like the opposite could be the case.
C) might be relevant if we were trying to compare Monrovia’s crime rate with Abstania’s, but we don’t have even close to enough information to make that comparison, so it’s irrelevant.
D) just adds a bit of zest to to the increase in the number of crimes. It has nothing to do with the argument, which hinges on connecting this increase with the migration.
E) is, in fact, closest to the problem with this argument mentioned in 2) above. If the argument had stated, “The unavoidable conclusion is that Monrovians were responsible for this increase”, without the phrase, “who migrated from Monrovia to Abstania”, then E would be a decent weakener. As it is, the argument isn’t even clearly asserting that the number of Monrovians in Abstania has increased. Maybe the overall number of Monrovians in Abstania decreased, but in 1998 a fleet of gangster motorcycle rebels come from Monrovia, a really bad lot, and they caused the crime. So E) is not a critical assumption of the argument, as it stands. Nevertheless, it is the best weakener, since it does give us a bit more information toward actually being able to compare the crime rates.
Weaken and strengthen questions won’t always attack a critical assumption in the argument, so the fact that a critical assumption isn’t addressed in these answer choices is not necessarily untestlike. I wouldn’t be too worried if you found this problem perplexing, however – especially if you were mindful of points 1) through 3) above.
Andrew Mitchell
GMAT Instructor
Assistant Director of GMAT & GRE
Kaplan Test Prep and Admissions
