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On a certain road 10% of the motorists exceed the posted spe

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Re: On a certain road 10% of the motorists exceed the posted spe [#permalink]

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New post 16 Jul 2013, 08:52
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Re: On a certain road 10% of the motorists exceed the posted spe [#permalink]

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New post 17 Jul 2013, 08:24
I agree that the level of a question depends on real gmat test takers' results. But imho this tag on a forum shouldnt be assessed by the level of only current gmatclub users, since perhaps current guys can be math genious or vise versa dummies like me:)

So , i wanted Bunuel to assess the level of a question, using his experience. He solved lots of gmat questions and knows well all ins&outs of this test. I feel better when i see his assessment rather than the one generated by some unknown to me users.

Anyways, i dont insist on anything. It is ur forum and ur rules. I just expressed my thoughts as a user and hope didnt offend anyone.

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Last edited by LalaB on 17 Jul 2013, 08:31, edited 1 time in total.
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New post 17 Jul 2013, 08:28
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On a certain road 10 percent of the motorists exceed the pos [#permalink]

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New post 10 Sep 2013, 01:55
On a certain road 10 percent of the motorists exceed the posted speed limit and receive speeding tickets, but 20 percent of the motorists who exceed the posted speed limit do not receive speeding tickets. What percent of the motorists on the road exceed the posted speed limit?

(A) 10 1/2%
(B) 12 1/2%
(C) 15%
(D) 22%
(E) 30%

It is an old OG problem that has not been explained clearly before. Please provide a detailed solution to the problem.

On another note, I notice that the overlapping sets are very often tested in this fairly confusing way, where I personally feel I am unable to use the grid advocated by MGMAT or Venn Diagram for that matter. I'm wasting plenty of time on setting it up. Any other methods you guys suggest to solve these? Or should I just "think better":)

Since this is the last problem of the set I presume it to be a 700+ level question, but it seems to me that in general GMAT is much harder these days that it was 10 years ago, so I'd guess it is hardly a 650 level today. Share your thoughts.
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Re: On a certain road 10 percent of the motorists exceed the pos [#permalink]

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New post 10 Sep 2013, 02:03
I think I got it with the grid...:)
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Re: On a certain road 10 percent of the motorists exceed the pos [#permalink]

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New post 10 Sep 2013, 03:00
Expert's post
obs23 wrote:
On a certain road 10 percent of the motorists exceed the posted speed limit and receive speeding tickets, but 20 percent of the motorists who exceed the posted speed limit do not receive speeding tickets. What percent of the motorists on the road exceed the posted speed limit?

(A) 10 1/2%
(B) 12 1/2%
(C) 15%
(D) 22%
(E) 30%

It is an old OG problem that has not been explained clearly before. Please provide a detailed solution to the problem.

On another note, I notice that the overlapping sets are very often tested in this fairly confusing way, where I personally feel I am unable to use the grid advocated by MGMAT or Venn Diagram for that matter. I'm wasting plenty of time on setting it up. Any other methods you guys suggest to solve these? Or should I just "think better":)

Since this is the last problem of the set I presume it to be a 700+ level question, but it seems to me that in general GMAT is much harder these days that it was 10 years ago, so I'd guess it is hardly a 650 level today. Share your thoughts.


Merging similar topics. Please refer to the different approaches offered on page 1 and ask if anything remain unclear.
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Re: On a certain road 10% of the motorists exceed the posted spe [#permalink]

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New post 23 Sep 2014, 06:38
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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On a certain road 10% of the motorists exceed the posted spe [#permalink]

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New post 14 Aug 2015, 07:00
Quote:
On a certain road 10 percent of the motorists exceed the posted speed limit and receive speeding tickets, but 20 percent of the motorists who exceed the posted speed limit do not receive speeding tickets. What percent of the motorists on the road exceed the posted speed limit?

(A) 10 1/2%
(B) 12 1/2%
(C) 15%
(D) 22%
(E) 30%


I don't know whether it's just me, but I find the wording of this question to be horrible. I actually got it right and came to 12,5%. Nevertheless, at least from my understanding the question looks for something completely different, namely - ''What percent of the motorists on the road exceed the posted speed limit?". So the question is rather looking for a comparison between motorists that exceed the limit and such that don't. Here we rather compare those that got tickets to the ones that didn't.

Am I the only one with this doubt or is it a way that exam makers want to confuse you?

Thanks!
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Last edited by bgpower on 18 Aug 2015, 00:37, edited 1 time in total.
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Re: On a certain road 10% of the motorists exceed the posted spe [#permalink]

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New post 18 Aug 2015, 00:31
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bgpower wrote:
Quote:
On a certain road 10 percent of the motorists exceed the posted speed limit and receive speeding tickets, but 20 percent of the motorists who exceed the posted speed limit do not receive speeding tickets. What percent of the motorists on the road exceed the posted speed limit?

(A) 10 1/2%
(B) 12 1/2%
(C) 15%
(D) 22%
(E) 30%


I don't know whether it's just me, but I find the wording of this question to be horrible. I actually got it right and came to 12,5%. Nevertheless, at least from my understanding the question looks for something completely different, namely - ''What percent of the motorists on the road exceed the posted speed limit?". So the question is rather looking for a comparison between motorists that exceed the limit and such that don't. Here we rather compare those that got tickets to the ones that didn't.

Am I the only one with this doubt or is it a way that exam makers what to confuse you?

Thanks!


The question is fine.

Some fraction of the motorists exceed the speed limit. Say x%. We need to find x%.

Some of these x% motorists get speeding tickets (say y%) and others do not. Anyone who gets a speeding ticket (belongs to y%) must belong to these x%.

You are given that y% of x% of Total motorists = 10% of Total motorists (people who exceed the limit and get tickets)

Also, 20% of x% do not get tickets. This means 80% of x% do get tickets.

This 80% of x% of Total= 10% of Total (we are already given)

So x% of Total = 12.5% of Total
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Re: On a certain road 10% of the motorists exceed the posted spe [#permalink]

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New post 31 Oct 2015, 12:24
let's say we have 100 motorists
10 received tickets for speeding.
we know that 0.2 of the total people who were speeding did not receive tickets.
that means that 10+0.2y = y, where y stands for all people who were speeding.
10 = 0.8y -> rewrite 10*10/8 = 100/8 = 25/2 = 12.5. B.
Re: On a certain road 10% of the motorists exceed the posted spe   [#permalink] 31 Oct 2015, 12:24

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