CR # 78 Source: OG

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focusgmat: Junior | Next Rank: 30 Posts; Posts: 28; Joined: Thu Apr 15, 2010 1:05 am

by focusgmat » Wed Jul 14, 2010 9:26 am

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.

I was split between choice B and D. Can someone explain why D is not the right answer ?

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Source: Beat The GMAT — Critical Reasoning | Wed Jul 14, 2010 9:26 am

ayushiiitm: Master | Next Rank: 500 Posts; Posts: 216; Joined: Wed Jul 23, 2008 2:35 am; Location: Pune, India; Thanked: 5 times; GMAT Score:700

by ayushiiitm » Wed Jul 14, 2010 10:00 am

focusgmat wrote: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.

I was split between choice B and D. Can someone explain why D is not the right answer ?

You are asked to find assumption

So first find the conclusion (c)
(C) drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are driver who do not.

the premises are
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.

so conclusion is based on the report that these ppl are ticketed more
but does getting ticketed more means exceeding the limit and it is not that they are ticketed more due to some other reason such as tracked more easily, or get noticed more
now assumption can fill a logical gap here

B says 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.

i.e who are ticketed for exceeding limit are actually exceeding limit

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paes: Legendary Member; Posts: 995; Joined: Tue Apr 13, 2010 11:56 pmFollowed by: 1 member; Thanked: 31 times

by paes » Wed Jul 14, 2010 6:09 pm

I am not able to understand how D is the assumption.

For a argument to be valid, the assumption must be true.
But even if d is false, argument makes sense.

take negation of D [ Kaplan method ]

Many of the vehicles that were ticketed for exceeding the speed limit were ticketed only once in the time period covered by the report.

e.g.
Suppose there are total 1000 vehicles.

then

vehicles with Radar : 30

Suppose 21 vehicles are ticketed
-- then 30% means 7 vehicle are with radar detector.

Based on above, we can conclude that :

drivers who equip their vehicles with radar detectors are more likely to get ticket or
hence more likely to exceed the speed limit.

[ so negation D : Many of the vehicles that were ticketed for exceeding the speed limit were ticketed only once in the time period covered by the report. ] - argument is still valid

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focusgmat: Junior | Next Rank: 30 Posts; Posts: 28; Joined: Thu Apr 15, 2010 1:05 am

by focusgmat » Thu Jul 15, 2010 5:49 am

I am still not clear on this question.

From the premises:

a)Only 3 percent of drivers on Maryland highways equipped their vehicles with radar detectors
Let no.of drivers in Maryland = 100
then 3% of 100 = 3 drivers equipped their vehicles ( 1 vehicle or more per each driver). Hence , greater than or = 3 vehicles in total equipped with radar detectors

b)33 percent of all vehicles ticketed for exceeding the speed limit were equipped with them :
No.of vehicles ticketed for exceeding speed limit with radar detectors can vary right from 1 vehicle to n vehicles

Option D :

If b) =1 then answer choice D is not true

Option B:

Negation method (when answer choice is negated it should weaken the conclusion)

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.

Please tell me how the negation method given in Kaplan or CR bible apply for option B.

How the above negation is weakening the following conclusion.
drivers who equip their vehicles with radar detectors are more likely to exceed the speed limit regularly than are driver who do not.

Please help.

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