A recent report determined that although only three percent of drivers on Maryland highways equipped their vehicles with radar detectors, thirty-three 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 drivers 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 the 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.
This CR exhibits a
language shift.
The premise is about drivers who get at least ONE -- and perhaps ONLY one -- speeding ticket.
The conclusion is about drivers who exceed the speed limit REGULARLY.
The argument assumes that there is a LINK between these two ideas: that a driver who gets at least ONE speeding ticket exceeds the speed limit REGULARLY.
The correct answer choice is WHAT MUST BE TRUE for the conclusion to be valid.
Apply the NEGATION TEST.
When the correct answer choice is REVERSED, the conclusion will be invalidated.
Any answer choice that fails this test can be eliminated.
Answer choice
B negated:
Drivers who are ticketed for exceeding the speed limit are LESS likely to exceed the speed limit regularly than are drivers who are not ticketed.
The negation of
B invalidates the conclusion that drivers with radar detectors speed regularly.
Thus,
B is the assumption: WHAT MUST BE TRUE for the conclusion to be valid.
The correct answer is
B.
C, negated:
The number of vehicles that were ticketed for exceeding the speed limit was not greater than the number of vehicles that were equipped with radar detectors.
This negation allows for the following case:
100 vehicles were ticketed for speeding, and each of these 100 vehicles had a radar detector.
The case above seems to STRENGTHEN the conclusion that
drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit.
Since the negation of C does not invalidate the conclusion, eliminate C.
Some students incorrectly select D.
D, negated:
Many of the vehicles that were ticketed for exceeding the speed limit were NOT ticketed more than once.
Implication:
All of the other ticketed vehicles WERE ticketed more than once.
Here, the vehicles that received multiple tickets could STRENGTHEN the conclusion that drivers with radar detectors speed regularly.
Since the negation of D does not invalidate the conclusion, eliminate D.
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