Bunuel
City resident: This year, the percentage of accidents caused by drivers ignoring traffic lights has fallen considerably. This means that the traffic police listened to our inquests regarding preventable traffic safety issues and took the measures needed to resolve the issues. Although accidents caused by other factors will not be eliminated, accidents that happen due to preventable traffic safety issues are certainly decreasing.
Of the following, which most clearly highlights a logical flaw in the reasoning of the city resident?
A. In reporting accidents caused due to drivers ignoring traffic light, the traffic police sometimes incorrectly attribute the accidents to a cause other than drivers ignoring traffic lights.
B. Accidents caused by factors other than drivers ignoring traffic lights could have risen sharply in number during the relevant year.
C. It is possible that inquests made with the traffic police are not the most reliable way to ascertain how many accidents took place in a particular year.
D. The accidents caused by other factors may have increased the number of inquests made with the traffic police.
E. In some accidents caused due to drivers ignoring traffic light, city residents many not believe that drivers ignoring traffic lights was the cause of the accidents.
Experts' Global Explanation: Mind-map: Percentage of accidents caused by drivers ignoring traffic lights declined this year à resident inquests regarding preventable traffic safety issues are addressed by traffic police à accidents caused by other factors will remain à accidents that happen due to preventable traffic safety issues are decreasing (conclusion)
Missing-link: Between percentage of accidents caused by drivers ignoring traffic lights declining this year and the conclusion that accidents that happen due to preventable traffic safety issues are decreasing
Expectation from the correct answer choice: Something on the lines of confusing the decline in the “percentage” of accidents of a particular type, among all accidents, with the decline in the “number” of the accidents of that type
Note: This argument commits the
classic GMAT error of confusing “percentage" with "absolute numbers”; the city resident cites the decline in the “percentage” of accidents of a particular type, among all accidents, but draws a conclusion about the decline in the “number” of the accidents of that type. Besides, please be extra careful when you see numbers/percentages/proportions in CR questions; often, the key lies in the numbers.
A. Trap. This answer choice, suggesting that some accidents are likely not correctly attributed to drivers ignoring traffic lights, indicates underreporting of such accidents; this answer choice makes no suggestion regarding a specific timeline, suggesting that this answer choice indicates
underreporting at all times in the past; so, underreporting is a
common factor in the past years and in this year, thus failing to explain any difference in the proportion/number of such accidents in this year; hence, this answer choice is
just additional information and does not weaken the argument. Furthermore, the flaw in the argument is that it confuses the decline in the “percentage” of accidents of a particular type, among all accidents, with the decline in the “number” of the accidents of that type; we need an answer choice on similar lines. Because this answer choice does not indicate the flaw in the argument, this answer choice is incorrect.
B.
Correct. If there is a sharp rise in the number of accidents because of factors other than drivers ignoring traffic lights, the number of all accidents is likely to rise significantly; a
large increase in the total number of accidents indicates that
even if the percentage of accidents of a particular type declined, it
does not necessarily indicate a decline in the number of such accidents (example: 10% of 100 is greater than 8% of 150); so, the possibility stated in this answer choice casts doubt on the conclusion that accidents that happen due to preventable traffic safety issues are decreasing; hence, failure to consider the sharp rise in the accidents caused by other factors is the flaw in the argument, as the answer choice mentions. Because this answer choice indicates the flaw in the argument, this answer choice is correct.
C. Trap. The argument is concerned with whether the accidents that happen due to preventable traffic safety issues are decreasing; the city resident cites inquests as the cause for this decline and
not as a measure of the number of accidents;
whether inquests are the most reliable way to ascertain the number of accidents
has no bearing on the argument; so, failure to consider the possibility stated in this answer choice is not the flaw in the argument. Furthermore, the flaw in the argument is that it confuses the decline in the “percentage” of accidents of a particular type, among all accidents, with the decline in the “number” of the accidents of that type; we need an answer choice on similar lines. Because this answer choice does not indicate the flaw in the argument, this answer choice is incorrect.
D. Trap. The argument is concerned with whether the accidents that happen due to preventable traffic safety issues are decreasing; the city resident cites inquests as the cause for this decline;
whether the number of inquests increased and what the cause for the increase was have no bearing on the argument; so, failure to consider the possibility stated in the answer choice is not the flaw in the argument. Furthermore, the flaw in the argument is that it confuses the decline in the “percentage” of accidents of a particular type, among all accidents, with the decline in the “number” of accidents of that type; we need an answer choice on similar lines. Because this answer choice does not indicate the flaw in the argument, this answer choice is incorrect.
E. Trap. What the city residents believe regarding particular accidents and their causes makes
no suggestion regarding whether the accidents that happen due to preventable traffic safety issues are decreasing; so, this answer choice is
just additional information and does not weaken the argument; hence, failure to consider the possibility stated in the answer choice is not the flaw in the argument. Furthermore, the flaw in the argument is that it confuses the decline in the “percentage” of accidents of a particular type, among all accidents, with the decline in the “number” of the accidents of that type; we need an answer choice on similar lines. Because this answer choice does not indicate the flaw in the argument, this answer choice is incorrect.
B is the best choice.