OG 11 ----81

Expert replies

schumi_gmat: Master | Next Rank: 500 Posts; Posts: 377; Joined: Wed Sep 03, 2008 9:30 amFollowed by: 2 members; Thanked: 15 times

by schumi_gmat » Thu Jun 11, 2009 6:06 pm

Q. 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.

OA is [spoiler](B)[/spoiler].

I know why OA is correct.
Can anyone explain why D is wrong?

Source: Beat The GMAT — Critical Reasoning | Thu Jun 11, 2009 6:06 pm

tohellandback: Legendary Member; Posts: 752; Joined: Sun May 17, 2009 11:04 pm; Location: Tokyo; Thanked: 81 times; GMAT Score:680

by tohellandback » Thu Jun 11, 2009 6:32 pm

I look forward to the explanation to this one..

The powers of two are bloody impolite!!

mikeCoolBoy: Master | Next Rank: 500 Posts; Posts: 119; Joined: Tue Jan 20, 2009 10:16 pm; Thanked: 9 times; GMAT Score:730

by mikeCoolBoy » Thu Jun 11, 2009 11:02 pm

I came across this problem yesterday and I also picked D. I'm also looking forward to the explanation because the one in the OG did not convince me.

turbo jet: Master | Next Rank: 500 Posts; Posts: 154; Joined: Mon Jun 08, 2009 10:02 pmFollowed by: 3 members; Thanked: 5 times

Why D is eliminated?

by turbo jet » Fri Jun 12, 2009 2:30 am

Explanation for eliminating D:Use Negating the Assumption Method

1. What is my conclusion:
Likeliness of crossing speed: By Radar equipped vehicle drivers MORE than non radar equipped vehicles
or paraphhrased to No of radar equipped drivers speeding> No of non radar equipped drivers speeding

2. Negate the assumption D:which tells us that
All cars that have been ticketed for crossing speed are ONE TIMER speed breakers.
The cars may be radar or non radar equipped.

3. Does my negated assumption undermine my conclusion?
No. It is neutral. I only know that all cars are one time speed breakers.
I cannot say anything about the no of cars of each type that sped drove.

Therefore eliminate D

However negating B assumption directly undermines my conclusion.

Hope this helps!!
Cheers
Turbo Jet

Life is Tom; I am Jerry

tanviet: Legendary Member; Posts: 1404; Joined: Tue May 20, 2008 6:55 pmFollowed by: 2 members; Thanked: 18 times

by tanviet » Mon Jun 15, 2009 9:04 pm

this one is hard for me first time but now I understand it

evidence, statistics must be representative for the conclusion to be good

hk: MBA Student; Posts: 532; Joined: Wed Jan 28, 2009 1:39 pmFollowed by: 9 members; Location: Barcelona; Thanked: 33 times; GMAT Score:640

by hk » Tue Jun 16, 2009 11:26 am

Here is another take on why to leave D alone!!!

The prompt says that only 3% of the drivers have radar and concludes that the drivers who have radar are prone to over speed.

Statement D says that most of the drivers who were ticketed for overspeeding were ticketed more than once. This statement talk about all of the drivers in general and does not talk about the ones who have radar --> which is the heart of the conclusion. Even logically speaking is its true that most of the drivers in Maryland were ticketed more than once, then probability of non-radar installed drivers (97% of population) to get a ticket twice is more. Hence this cannot be an assumption.

Hope i managed to type in whats in my mind

Wanna know what I'm upto? Follow me on twitter: https://twitter.com/harikrish

pink_08: Senior | Next Rank: 100 Posts; Posts: 87; Joined: Wed Dec 31, 2008 7:01 pm

Cr reasoning OG #81

by pink_08 » Thu Jul 02, 2009 8:19 pm

I am not sure how this works with actual numbers. Can someone please clarify. Example below :

3%of ( say 100,00 drivers in Maryland ) = 300

300 equipped with Radar

33% of ( 100 vehicles ticketed for exceeding speed limit ) = 33

# of Vehicles with radar > without radar, when it comes to exceeding speed limits

300 vehicles are MORE likely to exceed speed limits regularly than 99700

pink

vineetbatra: Master | Next Rank: 500 Posts; Posts: 355; Joined: Thu Feb 19, 2009 12:42 pmFollowed by: 1 member; Thanked: 2 times

Re: Why D is eliminated?

by vineetbatra » Sat Oct 03, 2009 3:25 pm

turbo jet wrote:Explanation for eliminating D:Use Negating the Assumption Method

1. What is my conclusion:
Likeliness of crossing speed: By Radar equipped vehicle drivers MORE than non radar equipped vehicles
or paraphhrased to No of radar equipped drivers speeding> No of non radar equipped drivers speeding

2. Negate the assumption D:which tells us that
All cars that have been ticketed for crossing speed are ONE TIMER speed breakers.
The cars may be radar or non radar equipped.

3. Does my negated assumption undermine my conclusion?
No. It is neutral. I only know that all cars are one time speed breakers.
I cannot say anything about the no of cars of each type that sped drove.

Therefore eliminate D

However negating B assumption directly undermines my conclusion.

Hope this helps!!
Cheers
Turbo Jet

Hi can you please explain how Assumption Negation will work with B.

Thanks,

Vineet

james33: Master | Next Rank: 500 Posts; Posts: 200; Joined: Sat Aug 22, 2015 10:27 am

by james33 » Sun May 15, 2016 9:37 pm

I will Go with option D in this case.

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