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

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

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16 Jun 2010, 08:31
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Question Stats:

67% (01:44) correct 33% (01:25) wrong based on 509 sessions

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On a certain road 10% of the motorists exceed the posted speed limit and receive speeding tickets, but 20% 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. 10.5%
B. 12.5%
C. 15%
D. 22%
E. 30%
[Reveal] Spoiler: OA

Last edited by Bunuel on 22 Jan 2013, 05:15, edited 1 time in total.
Renamed the topic and edited the question.

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Re: need help on % question [#permalink]

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16 Jun 2010, 08:40
If you give a value for the motorist .. x=100

then
10% exceed/ticketed = 10
20% exceed/not ticketed = 20

since they were either ticketed or not ticketed, all options have been covered; you have 30 total people that have exceeded the speed limit. This is 30% of 100.

IMO: E

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Re: need help on % question [#permalink]

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16 Jun 2010, 08:57
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chintzzz wrote:
On a certain road 10% of the motorists exceed the posted speed limit and receive speeding tickets, but 20% 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. 10.5%
B. 12.5%
C. 15%
D. 22%
E. 30%

Say there are 100 motorists.

{# of motorists who exceed speed & receive tickets} + {# of motorists who exceed speed & don't receive tickets} = {Total # of motorist who exceed speed};

Given: {# of motorists who exceed speed & receive tickets}=10;

Also, if {Total # of motorist who exceed speed}=x, then 0.2x={# of motorists who exceed speed & don't receive tickets};

$$10+0.2x=x$$ --> $$x=12.5$$.

Hope it's clear.
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Re: need help on % question [#permalink]

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16 Jun 2010, 10:55
chintzzz wrote:
On a certain road 10% of the motorists exceed the posted speed limit and receive speeding tickets, but 20% 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%

z= total motorists
y=motorists who speed and dont get ticket = y
motorists who speed = x =.1z+y
We are told that .2x=y

x=.1z+.2x -> .8x=.1z -> x=1/8z or 12.5%

B

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27 Feb 2011, 19:46
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On a certain road, 10 percent of the motorists exceed the posted speed limit and receive speeding tickets, but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets. What percent of the motorists on that road exceed the posted speed limit?

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

Read one line at a time and analyze it.

On a certain road, 10 percent of the motorists exceed the posted speed limit and receive speeding tickets,

>>>>10% of total motorists exceed speed limit and get tickets

but 20% of the motorists who exceed the posted speed limit do not receive speeding tickets.

>>>>>>20% who exceed the speed limit do not get tickets. Then 80% who exceed the speed limit must be getting tickets.

What percent of the motorists on that road exceed the posted speed limit?

>>>>> So 10% of total motorists = 80% of those who exceed speed limit
So those who exceed speed limits are 1/8 = 12.5% of the motorists
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Kudos [?]: 18147 [6], given: 236 TOEFL Forum Moderator Joined: 16 Nov 2010 Posts: 1589 Kudos [?]: 607 [0], given: 40 Location: United States (IN) Concentration: Strategy, Technology Re: need help on % question [#permalink] ### Show Tags 27 Feb 2011, 22:02 0.1 M = 0.80 E => E/M = 1/8 * 100 = 12.5% So answer is B. M - # of Motorists E - # of Motorists exceeding speed _________________ Formula of Life -> Achievement/Potential = k * Happiness (where k is a constant) GMAT Club Premium Membership - big benefits and savings Kudos [?]: 607 [0], given: 40 Director Status: Impossible is not a fact. It's an opinion. It's a dare. Impossible is nothing. Affiliations: University of Chicago Booth School of Business Joined: 03 Feb 2011 Posts: 866 Kudos [?]: 405 [5], given: 123 Re: need help on % question [#permalink] ### Show Tags 28 Feb 2011, 00:55 5 This post received KUDOS Using double matrix. Attachments percentage.jpg [ 21.09 KiB | Viewed 7574 times ] Kudos [?]: 405 [5], given: 123 Senior Manager Joined: 28 Aug 2010 Posts: 259 Kudos [?]: 808 [0], given: 11 Re: need help on % question [#permalink] ### Show Tags 09 Mar 2011, 16:49 80 % = 10% means 1/8 x100 = 12.5 _________________ Verbal:new-to-the-verbal-forum-please-read-this-first-77546.html Math: new-to-the-math-forum-please-read-this-first-77764.html Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html ------------------------------------------------------------------------------------------------- Ajit Kudos [?]: 808 [0], given: 11 Director Joined: 01 Feb 2011 Posts: 706 Kudos [?]: 150 [0], given: 42 Re: need help on % question [#permalink] ### Show Tags 09 Mar 2011, 19:59 Good question (10/100)(M) = E & get tickets (20/100)(E) = no tickets (80/100)(E) = tickets (80/100)E = (10/100)M => E = (10/80)M = 12.5% of M Answer is B. Kudos [?]: 150 [0], given: 42 Intern Joined: 29 Sep 2010 Posts: 7 Kudos [?]: [0], given: 3 Re: need help on % question [#permalink] ### Show Tags 10 Mar 2011, 02:58 I've solved via some kind of hybrid method. Out of 100 drivers, 10 receive a ticket. Those represent 80% of drivers who exceed the speed limit, denominated by $$X$$. Thus follows: $$X * 0,8 = 10$$ $$X = \frac{10}{0,8}$$ $$X = \frac{100}{8}$$ $$X = 12,5$$ => $$\frac{12,5}{100} = 0,125 = 12,5%$$ (B) Kudos [?]: [0], given: 3 Senior Manager Joined: 29 Jan 2011 Posts: 336 Kudos [?]: 248 [0], given: 87 Re: need help on % question [#permalink] ### Show Tags 04 Nov 2011, 01:17 Bunuel wrote: chintzzz wrote: On a certain road 10% of the motorists exceed the posted speed limit and receive speeding tickets, but 20% 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% Let's assume total # of motorists to be 100. {# of motorists who exceed speed & receive tickets} + {# of motorists who exceed speed & don't receive tickets} = {Total # of motorist who exceed speed}; Given: {# of motorists who exceed speed & receive tickets}=10; Also, if {Total # of motorist who exceed speed}=x, then 0.2x={# of motorists who exceed speed & don't receive tickets}; $$10+0.2x=x$$ --> $$x=12.5$$. Answer: B. Hope it's clear. i dont understand why cant it be 20 + 0.1 x = x?? as in how do we know we pick 10 for 10% of people who exceeded speed and received tickets and not equate it to 0.1 x = # of people who received tickets ??? we have taken 0.2 x as no. of people who speeded but dd not receive tickets ... so we should have similarly done for 10% of people who exceeded speed and received tickets which is 0.1 x but bunnels explanation just picks a number 10 so i am confused Kudos [?]: 248 [0], given: 87 Manager Joined: 29 Oct 2011 Posts: 180 Kudos [?]: 164 [0], given: 19 Concentration: General Management, Technology Schools: Sloan '16 (D) GMAT 1: 760 Q49 V44 GPA: 3.76 Re: need help on % question [#permalink] ### Show Tags 05 Nov 2011, 18:15 siddhans wrote: kostyan5 wrote: I concur with 12.5%. Kostyan5 can you please explain in detail how did you get to your answer? If 20% of the motorist who exceeded the speed limit did not get a ticket, then 80% of the motorist who exceeded the speed limit got a ticket. We are also told that 10% of all motorist exceed the limit and get tickets. So 10% of all motorists and 80% of motorist who exceeded the limit refer to the same group of people (exceeded and were ticketed). $$10% = 80% * motorist who exceeded$$ $$motorists who exceeded = \frac{10}{80} =.125 or 12.5%$$ Kudos [?]: 164 [0], given: 19 Director Joined: 29 Nov 2012 Posts: 862 Kudos [?]: 1492 [0], given: 543 Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 01:11 chintzzz wrote: On a certain road 10% of the motorists exceed the posted speed limit and receive speeding tickets, but 20% 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. 10.5% B. 12.5% C. 15% D. 22% E. 30% This is an overlapping set question Given 10 percent of motorists exceed speed limit and receive tickets Receive Tickets don't receive tickets Exceed 10 20/100X X Don't Exceed Let the total number for those who exceed be X then 20 percent of those received no tickets When we solve we get 10 + $$\frac{20}{100 X}$$ = X When we solve we get Answer B _________________ Click +1 Kudos if my post helped... Amazing Free video explanation for all Quant questions from OG 13 and much more http://www.gmatquantum.com/og13th/ GMAT Prep software What if scenarios http://gmatclub.com/forum/gmat-prep-software-analysis-and-what-if-scenarios-146146.html Kudos [?]: 1492 [0], given: 543 Senior Manager Joined: 23 Oct 2010 Posts: 380 Kudos [?]: 412 [0], given: 73 Location: Azerbaijan Concentration: Finance Schools: HEC '15 (A) GMAT 1: 690 Q47 V38 Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 04:15 Sorry for offtop- Can you please tell me whether you also edit the level of questions? I mean this question is marked as 700level, but I have some doubts about that. could you please also give me a link to Suggestions topic? I have some ideas. _________________ Happy are those who dream dreams and are ready to pay the price to make them come true I am still on all gmat forums. msg me if you want to ask me smth Kudos [?]: 412 [0], given: 73 Math Expert Joined: 02 Sep 2009 Posts: 42647 Kudos [?]: 135916 [0], given: 12716 Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 05:14 LalaB wrote: Sorry for offtop- Can you please tell me whether you also edit the level of questions? I mean this question is marked as 700level, but I have some doubts about that. could you please also give me a link to Suggestions topic? I have some ideas. Difficulty level is somewhat subjective, notice though that 45% of the users answered the question incorrectly. What would you say the difficulty level of this question should be? _________________ Kudos [?]: 135916 [0], given: 12716 Senior Manager Joined: 23 Oct 2010 Posts: 380 Kudos [?]: 412 [0], given: 73 Location: Azerbaijan Concentration: Finance Schools: HEC '15 (A) GMAT 1: 690 Q47 V38 Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 07:22 Imho it is 600 level I have read once that 700level question is the one that needs at least 2 steps to be solved or the one that covers hard topics like combinatorics etc Actually i didnt mean anything bad. I am not a math guru at all (unfortunately hehe) and have no right to judge a question. All i want to know is that whether you Bunuel edit that "level" tag. I rely on ur experience. But sometimes i get confused by these tags and just wonder what you think and whether u pay attention to the tags Ok, now i know that u edit these tags too. Thnx for the information _________________ Happy are those who dream dreams and are ready to pay the price to make them come true I am still on all gmat forums. msg me if you want to ask me smth Kudos [?]: 412 [0], given: 73 Math Expert Joined: 02 Sep 2009 Posts: 42647 Kudos [?]: 135916 [1], given: 12716 Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 07:34 1 This post received KUDOS Expert's post LalaB wrote: Imho it is 600 level I have read once that 700level question is the one that needs at least 2 steps to be solved or the one that covers hard topics like combinatorics etc Actually i didnt mean anything bad. I am not a math guru at all (unfortunately hehe) and have no right to judge a question. All i want to know is that whether you Bunuel edit that "level" tag. I rely on ur experience. But sometimes i get confused by these tags and just wonder what you think and whether u pay attention to the tags Ok, now i know that u edit these tags too. Thnx for the information Actually you have the same right to judge as anyone else. In fact you can change the difficulty tag (or any other tag for that matter) if you strongly feel that it's not correct. As for this question, I concur, it's not 700 level, though let's wait some time and see how the stats change. P.S. Yes, I do pay attention to the tags and permanently review them. _________________ Kudos [?]: 135916 [1], given: 12716 Senior Manager Joined: 23 Oct 2010 Posts: 380 Kudos [?]: 412 [0], given: 73 Location: Azerbaijan Concentration: Finance Schools: HEC '15 (A) GMAT 1: 690 Q47 V38 Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 07:46 Bunuel, thanks for ur kind reply. Could u plz send me a link to the suggestion topic? As a user I have some minor suggestions.i tried to find that topic _________________ Happy are those who dream dreams and are ready to pay the price to make them come true I am still on all gmat forums. msg me if you want to ask me smth Kudos [?]: 412 [0], given: 73 Math Expert Joined: 02 Sep 2009 Posts: 42647 Kudos [?]: 135916 [0], given: 12716 Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 07:52 LalaB wrote: Bunuel, thanks for ur kind reply. Could u plz send me a link to the suggestion topic? As a user I have some minor suggestions.i tried to find that topic have-a-suggestion-post-it-here-76017.html Thanks in advance for any input you provide. _________________ Kudos [?]: 135916 [0], given: 12716 Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7799 Kudos [?]: 18147 [3], given: 236 Location: Pune, India Re: On a certain road 10% of the motorists exceed the posted spe [#permalink] ### Show Tags 16 Jul 2013, 20:10 3 This post received KUDOS Expert's post LalaB wrote: I have read once that 700level question is the one that needs at least 2 steps to be solved or the one that covers hard topics like combinatorics etc I would like to give my opinion on this statement: Let's think about how the GMAT software decides the level of a question (simplifying the process by saying that it allots a level number to each question instead of a difficulty graph). The difficulty level is assigned by the people who take the test and not by the question setters. You have experimental questions, right? They are there to estimate the difficulty level (among other things) of the new question. Say, most test takers spend 3-4 mins on a particular question and still get it wrong. The software is likely to assign it a high difficulty level. It doesn't matter how many steps it needed or the topic it tested. Some of the most tricky questions are from number properties which I think is extremely simple theoretically. So what defines the difficulty level? The perception of the people. Why are combinatorics questions usually considered hard? Because people assume they are hard - they could be extremely straight forward but the moment people see 'how many ways' or 'what is the probability', they tend to take a step back. Similarly, function questions are usually considered difficult because of the notation but if you get over that notation you will see that those questions are usually very simple with a step wise process. Also, the answer to a question may be apparent to you with no steps needed if you understand the basics very well. To many others, it might seem very tricky and they might work on it for 5 mins before arriving at the solution. Therefore, when you think about the level of a question, think of how people will perceive it (hard to do without any data and/or experience in this field) rather than what you feel about the question. You may be very good at a topic and hence may feel that a certain question is simple but many others may not share your opinion. At the end of the day, opinion of the masses is what decides the question level (which implies a huge opportunity to do well by being comfortable in questions people consider hard). _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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Re: On a certain road 10% of the motorists exceed the posted spe   [#permalink] 16 Jul 2013, 20:10

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