skim wrote:
To decrease the number of crimes in city Y, the city's Police Commissioner proposed taking some police officers from low-crime districts of the city and moving them to high-crime districts of the city. His proposal is based on city Y crime data that show that the number of crimes in any district of the city decreases when additional police officers are moved into that district.
The Police Commissioner's proposal depends on which of the following assumptions?
(A) City X experienced a drastic reduction in crime after implementing a proposal similar to that proposed by the Police Commissioner of city Y.
(B) The severity of crimes committed in any district of the city decreases when additional police officers are moved into that district.
(C) The number of crimes committed in all high-crime districts of city Y is more than triple the number of crimes committed in all low-crime districts of city Y.
(D) There are more low-crime districts than high-crime districts in city Y.
(E) Districts of the city from which police officers are removed do not experience significant crime increases shortly after the removal of those officers.
This question is part of the GMAT Club Critical Reasoning : Assumption" Revision Project. OFFICIAL EXPLANATION:
The Police Commissioner's proposal hopes to decrease the number of crimes in city Y by shifting police officers from low-crime to high-crime districts. His proposal is based on data that demonstrate that crime decreases when additional police officers are moved into a district. However, the data do not mention anything about the effect on the districts from which the police officers were removed. The commissioner's plan is based on the assumption that the movement of police officers will not have any adverse effects on the low-crime districts.
(A) While it is encouraging that a similar plan worked successfully in City X, this fact is certainly not essential for the success of the plan in City Y. The cities may be so different as to make the comparison meaningless. (B) The police commissioner's proposal is focused solely on decreasing the number of crimes in city Y. The severity of the crimes has no bearing on whether the commissioner's proposal will succeed or not.
(C) The actual numerical distinction between high and low-crime areas of the city is immaterial to the commissioner's proposal. For instance, if the number of crimes committed in all high crime districts was only double (instead of more than triple) the number of crimes committed in low crime districts, the proposal could still be valid.
(D) It would be practically beneficial to the commissioner's plan if there were more low crime than high crime districts in city Y. This would enable the movement of police officers to every high crime district. However, this is not necessary to achieve the commissioner's goal of decreasing the total number of crimes in city Y. Even if there were more high-crime districts than low-crime districts in city Y, police officers could still be shifted to some (though not all) high-crime districts, and thereby possibly reduce the total number of crimes in city Y.
(E) CORRECT. The police commissioner's proposal would not make sense if districts of the city from which police officers are removed experience significant crime increases shortly after the removal of those officers. This would at least partially, if not fully, negate the reduction in the number of crimes in the high-crime districts. This choice establishes that, in fact, the low-crime districts do NOT suffer from significant crime increases after the removal of some officers-- an essential assumption upon which the commissioner's proposal depends.