Author 
Message 
TAGS:

Hide Tags

Senior Manager
Joined: 08 Nov 2008
Posts: 254

Stations X and Y are connected by two separate, straight,
[#permalink]
Show Tags
29 Mar 2009, 20:09
Question Stats:
43% (01:04) correct 57% (01:08) wrong based on 830 sessions
HideShow timer Statistics
Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination? (1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. (2) Train Q averaged a speed of 55 miles per hour for the entire trip.
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
"CEO in making"




Math Expert
Joined: 02 Sep 2009
Posts: 49300

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
26 Sep 2010, 04:24
Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination? (1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. (2) Train Q averaged a speed of 55 miles per hour for the entire trip. (1) As P averaged 70 miles per hour at the time when the two trains passed, hence when they passed each other P traveled 2*70=140 miles, so for P it was 110 miles left to cover and for Q 140. P was closer to its destination. Sufficient. (2) Knowing average speed for entire trip won't help us to determine the distance either of train coverd at the time they passed each other (as the average speed at the time the met could have been different). Not sufficient. Answer: A.
_________________
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




Director
Joined: 14 Aug 2007
Posts: 690

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
29 Mar 2009, 20:55
tenaman10 wrote: (1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. (2) Train Q averaged a speed of 55 miles per hour for the entire trip.
1) When trains passed, train P had travelled 140 miles (while Q traveled 110 miles), so P was closer. suff. 2) We don't know whether Q's speed was "constant" over the entire journey. A for me.



Manager
Joined: 19 May 2008
Posts: 155
Location: Mumbai

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
29 Mar 2009, 21:16
Statement 1 is sufficient. We know that when the trains passed, P had reached a distance of 140 miles (based on 70 m/hr avg speed). Hence P was just 110 miles from destination  which means Q was farther away from its destination.
Statement 2  we know that after 2 hrs, train Q reached a distance of 110 miles  based on its avg speed throughout the journey  and also it took 4.5 hrs to reach destination. So as per the question, the 2 trains passed each other after 2 hrs, by which time Q had reached 110 miles, based on avg speed  so Q was farther from its destination.
Answer is D  both statements are sufficient on its own. What is the OA?



Manager
Joined: 19 May 2008
Posts: 155
Location: Mumbai

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
29 Mar 2009, 21:18
Actually it should be A  since we don't know that the avg speed of the train after 2 hrs was 55  we just know that Q avged 55 over the whole journey.



Manager
Joined: 22 Feb 2009
Posts: 128
Schools: Kellogg (R1 Dinged),Cornell (R2), Emory(Interview Scheduled), IESE (R1 Interviewed), ISB (Interviewed), LBS (R2), Vanderbilt (R3 Interviewed)

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
17 Apr 2009, 10:27
gmat911 wrote: why would you say it's A? A does not say anything about the other train. i think it's E since B does not tell you the speed when it was at 2 hours.... am i missing something? Q asks that which train is closer to its destination when they met. As per sta 1, A has already travelled 140KM. SO the remaining distance of 250 km is 110 KM which the train 2 must have travelled. Therefore, we need not required the speed of B to know is it is closer to its destination than A. Hope it expalins



Manager
Joined: 19 Aug 2006
Posts: 221

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
03 May 2009, 11:47
stmnt1 nsf, because we can't get anything from it other than time of 2 hours  it says 70mi/h at the time they passed, but who knows what was the speed of P before then; cannot get the distance traveled by P either for the same reason.
stmnt2 S(q)=55mi/h D(q)=250 miles t(q)=4.5h nsf  nothing about train P
Let's combine.
We can get the distance traveled by P by the time they met: t(p)=2h D(p)=250D(q)=140 miles
From here, it's easy to see that P was closer to its destination at the time the trains met.
So, C is the answer.



Director
Joined: 23 May 2008
Posts: 730

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
03 May 2009, 12:59
bandit wrote: gmat911 wrote: why would you say it's A? A does not say anything about the other train. i think it's E since B does not tell you the speed when it was at 2 hours.... am i missing something? Q asks that which train is closer to its destination when they met. As per sta 1, A has already travelled 140KM. SO the remaining distance of 250 km is 110 KM which the train 2 must have travelled. Therefore, we need not required the speed of B to know is it is closer to its destination than A. Hope it expalins statement 1 says that train A was going 70mph "at the time the two trains passed" what about before and after the trains passed. We need a constant or average speed to tell the distance travelled. insuff statement 2 gives us a constant speed for train Q so distance travelled was 110 miles. This is where they met so 250110=140, the distance P travelled, so P is closer to destination ans B IMO



Manager
Joined: 13 Jan 2009
Posts: 162
Schools: Harvard Business School, Stanford

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
20 Aug 2009, 00:02
It is not C, in my opinion. I go with E.
St 1. train P's speed 70mph at the time of trains pass each other, we can't determine it's speed before and after. Insuff. St 2. train Q's speed average of 55mph, we can't determine train B's speed at the time of two trains pass each other.
Combined, we also don't get anything, Hence E is the answer!



Manager
Joined: 05 Jul 2009
Posts: 141
Location: Australia
Schools: Chicago Booth class of 2012
WE 1: Consulting
WE 2: Small business/Start up
WE 3: Strategy  Large Corporate

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
21 Aug 2009, 22:18
I believe that (1) is sufficient, because it notes that:
(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour
Therefore after two hours with this average, the distance travelled would be 140. Def A.



Manager
Joined: 12 Aug 2009
Posts: 84

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
22 Aug 2009, 07:35
IMO  A . Becuase it says "had averaged" ....
It is tricky though. I hope GMAT does not test this kind of questions, where you need to pay so much attention.



Manager
Joined: 10 Jul 2009
Posts: 115
Location: Ukraine, Kyiv

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
20 Sep 2009, 06:06
IMO two statements are similar. what is the difference? think D. do not understand why is it C. what is the source? is OA right? the formula states: avg sp = total distance/total time. stmt1: train A in two hours made 140 miles, thus it is closer than B to the destination. suff stmt2: train B in two hours did 110 miles. thus train A is closer. suff can anyone post a clear explanation to this?
_________________
Never, never, never give up



Intern
Joined: 18 Sep 2009
Posts: 19

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
22 Sep 2009, 08:09
Hi,
I think this:
(1) It said that the train P had averaged a speed of 70 miles per hour, at the time the two trains passed. BUT, we don't know nothing about TRAIN Q. ( INSUFF.)
(2) Train Q, had averaged a speed 55 M/h for the ENTIRE TRIP. In that way,We know that Train Q, travelled 110 Miles in 2 hours (55 M/h * 2 hours). BUT, we dont know about the Train P. (INSUFF)
Well, (1) + (2) :
FOR (2): We know Train Q had traveled 110 miles and has to travel 140 miles, MORE!. FOR (1), At the same time, Train P, had speed average 70 Miles per hour BUT HAD ALREADY TRAVELLED 140 miles when passed Train Q and so, Train P only has 110 miles to travel. In that way, TRAIN P was nearer than Q.
ANSWER = C.
What to do you think guys?
Cheers!



Intern
Joined: 19 Aug 2009
Posts: 15

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
23 Sep 2009, 12:08
gmatpill wrote: Quote: Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination? (1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. (2) Train Q averaged a speed of 55 miles per hour for the entire trip.
So many different answers. I'm going to stick my head out and say the answer is (D). Here's why:(1) At the 2 hour mark, train P averaged 70 mph. After the 2 hr mark, the train could have sped up or slowed down, but at that 2 hour mark, train P averaged 70 mph for the previous 2 hours. That means it must have traveled 2*70 = 140 miles during that 2 hr period. Given that the entire trail is 250 miles, the midpoint is 125 miles. Clearly, train P passed the midpoint at the 140 mile mark. That means the remaining 110 must be the distance that the other train travelled. All we need to know is that train P passed the midpoint, that means it must be nearer to its destinationwhich means we have enough info to answer the quesiton!(2) Train Q averaging 55 mph for 2 hrs means it traveled 110 miles. 110 mile mark is less than the midpoint of the 250 mile trail (125 miles). T his means the OTHER train (P), must have traveled further and is therefore closer to its destination. So in this case, either (1) or (2) provides sufficient info to tell us which train was closer to its destination.Remember, the question TELLS you that you have a constant DISTANCE (250 miles) and a constant TIME (2 hrs) for you to do your analysis.
Remember the Rates Framework: There 3 components: Distance = Rate * Time. You have info on distance and time. All you need is some good info on rates. It turns out either statement (1) or (2) gives you good info on rates, so the answer is (D).I think you misread statement B  The train does not average 55 mph for 2 hours; it averaged 55 mph for the entire trip. This could mean that in the first two hours it may have traveled at any speed faster or slower than 55 mph, which would make the statement NSF. I strongly believe that the only suitable answer is A. Is there an explanation for the OA of C? Where did this question come from?



Manager
Joined: 25 Mar 2009
Posts: 52

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
24 Sep 2009, 09:43
gmatpill wrote: Quote: Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination? (1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. (2) Train Q averaged a speed of 55 miles per hour for the entire trip.
So many different answers. I'm going to stick my head out and say the answer is (D). Here's why:(1) At the 2 hour mark, train P averaged 70 mph. After the 2 hr mark, the train could have sped up or slowed down, but at that 2 hour mark, train P averaged 70 mph for the previous 2 hours. That means it must have traveled 2*70 = 140 miles during that 2 hr period. Given that the entire trail is 250 miles, the midpoint is 125 miles. Clearly, train P passed the midpoint at the 140 mile mark. That means the remaining 110 must be the distance that the other train travelled. All we need to know is that train P passed the midpoint, that means it must be nearer to its destinationwhich means we have enough info to answer the quesiton!(2) Train Q averaging 55 mph for 2 hrs means it traveled 110 miles. 110 mile mark is less than the midpoint of the 250 mile trail (125 miles). T his means the OTHER train (P), must have traveled further and is therefore closer to its destination. So in this case, either (1) or (2) provides sufficient info to tell us which train was closer to its destination.Remember, the question TELLS you that you have a constant DISTANCE (250 miles) and a constant TIME (2 hrs) for you to do your analysis.
Remember the Rates Framework: There 3 components: Distance = Rate * Time. You have info on distance and time. All you need is some good info on rates. It turns out either statement (1) or (2) gives you good info on rates, so the answer is (D).I don't think it's D, if D, it will be like this: Stations X and Y are connected by two separate, straight, parallel rail lines that are 250 miles long. Train P and train Q simultaneously left Station X and Station Y, respectively, and each train traveled to the other’s point of departure. The two trains passed each other after traveling for 2 hours. When the two trains passed, which train was nearer to its destination? (1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. (2) At the time when the two trains passed, Train Q averaged a speed of 55 miles per hour for the entire trip. It's easy to calculate but the point is the different of 1) with At the time when the two trains passed and 2)without phrase At the time when the two trains passed IT's subtle, anyone pls help explain the meaning.



Intern
Joined: 19 Oct 2009
Posts: 45

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
17 Nov 2009, 12:25
IMO A..
B is not sufficient because we don't know when the two trains meet. After 2 hrs means they can meet after 3, 4, 5 hrs etc...so if they meet exactly after 2 hrs, we know the answer but if they met after 4 hrs (which indeed can be the case : since 4 hrs are ofcourse after 2 hrs ), then we would get just opposite answer to what we get in case of 2 hrs.



Senior Manager
Affiliations: PMP
Joined: 13 Oct 2009
Posts: 270

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
Updated on: 17 Nov 2009, 15:23
(1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. if S1 (1) At the time when the two trains passed, train P had averaged a speed of 70 miles per hour. said instead (1) till the time when the two trains passed, train P had averaged a speed of 70 miles per hour. then we can take train P's speed as 70 for first 2 hours, otherwise, we cannot assume that. what is the source of the question ? Edited
_________________
Thanks, Sri  keep uppp...ing the tempo...
Press +1 Kudos, if you think my post gave u a tiny tip
Originally posted by srini123 on 17 Nov 2009, 12:50.
Last edited by srini123 on 17 Nov 2009, 15:23, edited 2 times in total.



Intern
Joined: 19 Oct 2009
Posts: 45

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
17 Nov 2009, 14:17
answer is A....gmat sets contain lots of wrong answer.... check this out http://www.manhattangmat.com/forums/ds ... t679.html



Intern
Joined: 25 Jan 2010
Posts: 5

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
29 Jan 2010, 06:30
From A we can deduce that passing time First train already passed 2*70km=140km And it mast pssed only 110km, But second train passed 110km. So Answer is A, From B we can deduce noting



Intern
Joined: 27 Aug 2010
Posts: 20

Re: DS Relative Speed  Set 14
[#permalink]
Show Tags
26 Sep 2010, 04:02
Consider the 2nd condition the following way: You are given the average of a set = 50. {40,50,60}, {10,50,90} are among many others that have the average of 50, including {50,50,50}. It means that the speed of the train could seriously differ during his travel and, therefore, we can't define the speed of train Q in a moment of time the trains have met.




Re: DS Relative Speed  Set 14 &nbs
[#permalink]
26 Sep 2010, 04:02



Go to page
1 2
Next
[ 27 posts ]



