Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 13 Oct 2010
Posts: 20

A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
13 Dec 2010, 01:26
Question Stats:
58% (01:53) correct 42% (01:54) wrong based on 462 sessions
HideShow timer Statistics
A circular racetrack is 3 miles in length and has signs posted to indicate each 1/10 mile increment. If a race car starts at a random location on the track and travels exactly one half mile, what is the probability that the car ends within a half mile of the sign indicating 2 1/2 miles? A. 1/6 B. 3/10 C. 1/3 D. 1/2 E. 2/3
Official Answer and Stats are available only to registered users. Register/ Login.




Math Expert
Joined: 02 Sep 2009
Posts: 47983

A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
13 Dec 2010, 04:13
helloanupam wrote: A circular racetrack is 3 miles in length and has signs posted to indicate each 1/10 mile increment. If a race car starts at a random location on the track and travels exactly one half mile, what is the probability that the car ends within a half mile of the sign indicating 2 1/2 miles?
A. 1/6 B. 3/10 C. 1/3 D. 1/2 E. 2/3
Bunuel, Sorry, I could not understand the language of the question and hence probably the answer is not clear to me. If possible , could you reframe the question or explain as to what the question is asking? Look at the diagram: The car ends within a half mile of the sign indicating 2.5 miles means that the car should end in one mile interval, between the signs indicating 2 (2.50.5=2) and 3 miles (2+0.5=3), so within the red segment on the diagram. Now if the car appears somewhere between the blue dots, between 1.5 and 2 miles signs then after traveling 0.5 miles the car will be in the red segment. So in order after traveling 0.5 miles the car to end within the red segment it should appear between 1.5 and 2.5 miles, so within 1 mile interval, as the circumference of the track is 3 miles then the probability of that will be P=favorable/total=1/3. As I mentioned in my previous post actually it doesn't matter where the car appears or what distance it travel, as long as favorable interval in the end is 1 mile and total interval is 3 miles then the probability will be 1/3 miles. Hope it's clear. Attachment:
untitled.PNG [ 5.9 KiB  Viewed 7198 times ]
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics




Math Expert
Joined: 02 Sep 2009
Posts: 47983

Re: Circular Race Track Probability.
[#permalink]
Show Tags
13 Dec 2010, 02:34
helloanupam wrote: A circular racetrack is 3 miles in length and has signs posted to indicate each 1/10 mile increment. If a race car starts at a random location on the track and travels exactly one half mile,what is the probability that the car ends within a half mile of the sign indicating 2 1/2 miles? (A) 1/6 (B) 3/10 (C) 1/3 (D) 1/2 (E) 2/3
Answer: C
Could somebody explain how to work this out? The car ends within a half mile of the sign indicating 2 1/2 miles means that the car will end in one mile interval, between the signs indicating 2 and 3 miles. Now, it doesn't matter where the car starts or what distance it travels, the probability will be P=(favorable outcome)/(total # of outcomes)=1/3 (as the car starts at random point end travels some distance afterwards we can consider its end point as the point where he randomly appeared, so the probability that the car appeared within 1 mile interval out of total 3 miles will be 1/3). Answer: C. Hope it's clear.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Intern
Joined: 13 Oct 2010
Posts: 20

Re: Circular Race Track Probability.
[#permalink]
Show Tags
13 Dec 2010, 03:47
Bunuel, Sorry, I could not understand the language of the question and hence probably the answer is not clear to me. If possible , could you reframe the question or explain as to what the question is asking?



Director
Joined: 03 Sep 2006
Posts: 835

Re: Circular Race Track Probability.
[#permalink]
Show Tags
13 Dec 2010, 05:06
Don't we somehow need to use the information 1/10 mile increment signposts in calculating the probability? Approach mentioned above is logical but there must be simple mathematical solution using the increment signposts?



Math Expert
Joined: 02 Sep 2009
Posts: 47983

Re: Circular Race Track Probability.
[#permalink]
Show Tags
13 Dec 2010, 06:14
LM wrote: Don't we somehow need to use the information 1/10 mile increment signposts in calculating the probability? Approach mentioned above is logical but there must be simple mathematical solution using the increment signposts? Stem gives us the information about the signs only to fix the point of 2.5 miles on the track and thus fix the 1 mile interval the car should end within. 1/10 mile increment is totally irrelevant. Consider the following: A circular racetrack is 3 miles in length. If a race car starts at a random location on the track and travels exactly Y miles, what is the probability that the car ends within a half mile of some point X on the track? The answer will be the same: as the interval for the endpoint of the car is 1 mile (from x0.5 to x+0.5) then the probability will be 1/3. Note that a car starts at a random location on the track and travels exactly Y miles means that the endpoint of the car will also be at random location on the track (travel part is also to confuse us: random location plus Y miles=random location). So the question basically ask what is the probability that the car ends within the particular 1 mile interval on the track of 3 miles. Hope it's clear.
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Senior Manager
Status: Bring the Rain
Joined: 17 Aug 2010
Posts: 358
Location: United States (MD)
Concentration: Strategy, Marketing
Schools: Michigan (Ross)  Class of 2014
GPA: 3.13
WE: Corporate Finance (Aerospace and Defense)

Re: Circular Race Track Probability.
[#permalink]
Show Tags
13 Dec 2010, 06:41



Intern
Joined: 13 Oct 2010
Posts: 20

Re: Circular Race Track Probability.
[#permalink]
Show Tags
13 Dec 2010, 08:37
Thankyou Bunuel for the extra efforts in explaining. I have now understood your explanation.



Math Expert
Joined: 02 Sep 2009
Posts: 47983

Re: A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
07 Jun 2013, 07:05



Intern
Joined: 09 Apr 2013
Posts: 40
Location: United States (DC)
Concentration: Strategy, Social Entrepreneurship
GPA: 3.55
WE: General Management (NonProfit and Government)

Re: A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
07 Jun 2013, 08:33
Here is a rewording of the original question: What is the probability that the car starts between the 1.5 mile and 2.5 mile mark on a 3 mi racetrack?
2.5  1.5 = 1 that is 1/3 of the racetrack
Answer is C
Everything else in this question is irrelevant. Although, if you really wanted you could rephrase the question to account for the 1/10th mile sign posts: What is the probability that the car stars between the 15th and 25th sign posts if there are 30 sign posts total. But that is unnecessary extra work.



Manager
Joined: 14 Nov 2011
Posts: 131
Location: United States
Concentration: General Management, Entrepreneurship
GPA: 3.61
WE: Consulting (Manufacturing)

Re: Circular Race Track Probability.
[#permalink]
Show Tags
09 Jun 2013, 05:44
Bunuel wrote: helloanupam wrote: Bunuel, Sorry, I could not understand the language of the question and hence probably the answer is not clear to me. If possible , could you reframe the question or explain as to what the question is asking? Look at the diagram: Attachment: untitled.PNG The car ends within a half mile of the sign indicating 2.5 miles means that the car should end in one mile interval, between the signs indicating 2 (2.50.5=2) and 3 miles (2+0.5=3), so within the red segment on the diagram. Now if the cars appears somewhere between the blue dots, between 1.5 and 2 miles signs then after traveling 0.5 miles the car will be in the red segment. So in order after traveling 0.5 miles the car to end within the red segment it should appear between 1.5 and 2.5 miles, so within 1 mile interval, as the circumference of the track is 3 miles then the probability of that will be P=favorable/total=1/3. As I mentioned in my previous post actually it doesn't matter where the car appears or what distance it travel, as long as favorable interval in the end is 1 mile and total interval is 3 miles then the probability will be 1/3 miles. Hope it's clear. Hi Bunnel, What about if car starts between 0.5 and 2.5 miles? So this will make probability = 2*1/3 ?



Target Test Prep Representative
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 3176
Location: United States (CA)

Re: A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
14 Feb 2017, 16:55
helloanupam wrote: A circular racetrack is 3 miles in length and has signs posted to indicate each 1/10 mile increment. If a race car starts at a random location on the track and travels exactly one half mile, what is the probability that the car ends within a half mile of the sign indicating 2 1/2 miles?
A. 1/6 B. 3/10 C. 1/3 D. 1/2 E. 2/3 We are given that a circular racetrack is 3 miles in length and has signs posted to indicate each 1/10 mile increment. We are also given that a race car starts at a random location on the track and travels exactly one half mile, and we need to determine the probability that the car ends within a half mile of the sign indicating 2 1/2 (or 2.5) miles. If the car ends within a half mile of the 2.5mile sign, that means the car can end as far as the 2.0mile sign or the 3.0mile sign. However, since the car travels exactly one half mile, the starting point of the car can be anywhere from the 1.5 mile sign to the 2.5mile sign. In other words, the car can be anywhere in this 2.5  1.5 = 1 mile stretch. Since the racetrack is 3 miles long, the probability that the car is in this 1 mile stretch is ⅓. Answer: C
_________________
Scott WoodburyStewart
Founder and CEO
GMAT Quant SelfStudy Course
500+ lessons 3000+ practice problems 800+ HD solutions



Senior Manager
Joined: 03 Apr 2013
Posts: 290
Location: India
Concentration: Marketing, Finance
GPA: 3

Re: A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
11 Jul 2017, 06:42
Bunuel wrote: helloanupam wrote: A circular racetrack is 3 miles in length and has signs posted to indicate each 1/10 mile increment. If a race car starts at a random location on the track and travels exactly one half mile,what is the probability that the car ends within a half mile of the sign indicating 2 1/2 miles? (A) 1/6 (B) 3/10 (C) 1/3 (D) 1/2 (E) 2/3
Answer: C
Could somebody explain how to work this out? The car ends within a half mile of the sign indicating 2 1/2 miles means that the car will end in one mile interval, between the signs indicating 2 and 3 miles. Now, it doesn't matter where the car starts or what distance it travels, the probability will be P=(favorable outcome)/(total # of outcomes)=1/3 (as the car starts at random point end travels some distance afterwards we can consider its end point as the point where he randomly appeared, so the probability that the car appeared within 1 mile interval out of total 3 miles will be 1/3). Answer: C. Hope it's clear. BunuelShouldn't the answer be 2/3? The question doesn't specify in which direction the car has to travel, so it could be in either direction. Or may be I'm overthinking
_________________
Spread some love..Like = +1 Kudos



Manager
Joined: 26 Dec 2017
Posts: 138

Re: A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
15 Jul 2018, 11:47
Bunuel wrote: helloanupam wrote: Bunuel, Sorry, I could not understand the language of the question and hence probably the answer is not clear to me. If possible , could you reframe the question or explain as to what the question is asking? Look at the diagram: Attachment: untitled.PNG The car ends within a half mile of the sign indicating 2.5 miles means that the car should end in one mile interval, between the signs indicating 2 (2.50.5=2) and 3 miles (2+0.5=3), so within the red segment on the diagram. Now if the car appears somewhere between the blue dots, between 1.5 and 2 miles signs then after traveling 0.5 miles the car will be in the red segment. So in order after traveling 0.5 miles the car to end within the red segment it should appear between 1.5 and 2.5 miles, so within 1 mile interval, as the circumference of the track is 3 miles then the probability of that will be P=favorable/total=1/3. As I mentioned in my previous post actually it doesn't matter where the car appears or what distance it travel, as long as favorable interval in the end is 1 mile and total interval is 3 miles then the probability will be 1/3 miles. Hope it's clear. BunuelA small doubt here to be precise the correct ranges would be 2.1,2.2,2.3,2.4,2.5,2.6,2.7,2.8,2.9 as 2.5 miles /+ 0.4 miles (within 0.5 miles i.e, <=0.5> <0.4) is between 2.1 and 2.9 probability would be 9/31. (31 0,0.1,....3.0) I know the above is wrong but I am having confusion with distance vs exact point transition.(In other words I am calculating exact point like 2.1,2.2,... as in question given 2.5 (within half mile) but unable to know how 23> as OS is capturing the exact condition of question) Pls help me to figure out where I faltered.
_________________
If you like my post pls give kudos



Intern
Joined: 10 Jul 2018
Posts: 4

Re: A circular racetrack is 3 miles in length and has signs post
[#permalink]
Show Tags
31 Jul 2018, 14:42
Shouldn't the question say "one half miles" instead of "one half mile"? Because "one half mile" can be read as one of 1/2 mile.




Re: A circular racetrack is 3 miles in length and has signs post &nbs
[#permalink]
31 Jul 2018, 14:42






