While on a straight road, Car X and Car Y are traveling at : GMAT Data Sufficiency (DS)
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# While on a straight road, Car X and Car Y are traveling at

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While on a straight road, Car X and Car Y are traveling at [#permalink]

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17 Mar 2012, 17:44
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Question Stats:

73% (02:01) correct 27% (01:21) wrong based on 907 sessions

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While on a straight road, Car X and Car Y are traveling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y ?

(1) Car X is traveling at 50 miles per hour and Car Y is traveling at 40 miles per hour.
(2) Three minutes ago Car X was 1/2 mile ahead of Car Y.
[Reveal] Spoiler: OA

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Last edited by Bunuel on 07 Dec 2012, 09:38, edited 1 time in total.
Renamed the topic and edited the question.
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17 Mar 2012, 20:22
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A follows B, Time to catchup = (Distance between A and B)/(SA - SB)

A)
SA - SB is the relative speed = 50-40=10 m/hr
Distance between A and B = 2-1 = 1.

Therefore, Time to catchup = 1/10 hours = 0.1*60 minutes = 6 mintues

Sufficient.

B)
3 minutes for 1/2 mile
Therefore 1 mile will be 6 minutes

Sufficient

Thus D.
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Re: While on a straight road, car X and car Y are traveling at [#permalink]

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18 Mar 2012, 06:21
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While on a straight road, Car X and Car Y are traveling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y ?

(1) Car X is traveling at 50 miles per hour and Car Y is traveling at 40 miles per hour --> since we have the rates of both cars and the distance between them we can calculate any other question regarding them. Sufficient.

(2) Three minutes ago Car X was 1/2 mile ahead of Car Y --> car X gains 1/2 mile in every 3 minutes (since now it's 1 mile ahead), hence it'll gain additional 1 mile in next 6 minutes. Sufficient.

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Re: While on a straight road, car X and car Y are traveling at [#permalink]

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11 Nov 2012, 00:54
Bro Bunuel,

How to solve this to get the time in secs if we consider this as 2 independent PS questions?

Regards,
Sachin
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Re: While on a straight road, car X and car Y are traveling at [#permalink]

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11 Nov 2012, 01:06
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ok.. i just figured out..

1)

relative speed: 10 miles/ hour = 1/6 miles / min
distance to be covered: 1 mile.

time taken : 1/(1/6) = 6 mins..

2)
find the rate :
distance : 1/2 mile
time taken: 3 mins

rate: 1/6 miles / min

now,
distance=1 mile
rate : 1/6 miles/ min

so time: 6 mins

hope it helps! ( Bunuel's statement )
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Re: While on a straight road, Car X and Car Y are traveling at [#permalink]

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01 Aug 2013, 12:00
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While on a straight road, Car X and Car Y are traveling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y ?

Car X is traveling at a greater speed/rate than Y.

(1) Car X is traveling at 50 miles per hour and Car Y is traveling at 40 miles per hour.

Car X is traveling at 5/6 miles/minute.
Car Y is traveling at 4/6 miles/minute.

Every minute, Car X moves away from car Y at a rate of (5/6) - (4/6) = 1/6 miles. Therefore, car X will have moved an additional mile away from car Y in six minutes.
SUFFICIENT

(2) Three minutes ago Car X was 1/2 mile ahead of Car Y.
In three minutes, car X managed to move 1/2 mile further away from Y. Because both cars were moving at constant rates, car x would have moved away from Y at a rate of 1/6 miles per minute, or 3/6 = 1/2 miles in three minutes. We know how long it takes x to move 1/2 mile from Y and because the speed of Y is constant, the rate at which x moves away from y will be constant as well.
SUFFICIENT

(D)
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Re: While on a straight road, Car X and Car Y are traveling at [#permalink]

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22 Oct 2013, 10:43
WholeLottaLove wrote:
While on a straight road, Car X and Car Y are traveling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y ?

Car X is traveling at a greater speed/rate than Y.

(1) Car X is traveling at 50 miles per hour and Car Y is traveling at 40 miles per hour.

Car X is traveling at 5/6 miles/minute.
Car Y is traveling at 4/6 miles/minute.

Every minute, Car X moves away from car Y at a rate of (5/6) - (4/6) = 1/6 miles. Therefore, car X will have moved an additional mile away from car Y in six minutes.
SUFFICIENT

(2) Three minutes ago Car X was 1/2 mile ahead of Car Y.
In three minutes, car X managed to move 1/2 mile further away from Y. Because both cars were moving at constant rates, car x would have moved away from Y at a rate of 1/6 miles per minute, or 3/6 = 1/2 miles in three minutes. We know how long it takes x to move 1/2 mile from Y and because the speed of Y is constant, the rate at which x moves away from y will be constant as well.
SUFFICIENT

(D)

Correction in the explanation.
Every minute, Car X moves away from car Y at a rate of (5/6) - (4/6) = 1/3 miles. Therefore, car X will have to travel for 6 mins to move 2 miles farther away from car Y..
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Re: While on a straight road, Car X and Car Y are traveling at [#permalink]

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18 May 2014, 09:56
Statement 1: Car X is traveling at 50 miles per hour and car Y is traveling at 40 miles per hour.
Notice that we could easily duplicate this scenario in real life.
Have Car X drive at 50 mph and car Y at 40mph.
Use a stopwatch to time how long it takes for Car X to be 2 miles ahead of Y.
As you can see, we have enough information to answer the target question
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Statement 2: 3 minutes ago car X was 1/2 mile ahead of car Y.
If car X is presently 1 mile ahead, we can see that car X gains 1/2 mile every 3 minutes.
At that rate, car X will gain another 1 mile in 6 minutes.
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Hence D
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While on a straight road, Car X and Car Y are traveling at [#permalink]

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02 May 2015, 11:55
Bunuel wrote:
While on a straight road, Car X and Car Y are traveling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y ?

(1) Car X is traveling at 50 miles per hour and Car Y is traveling at 40 miles per hour --> since we have the rates of both cars and the distance between them we can calculate any other question regarding them. Sufficient.

(2) Three minutes ago Car X was 1/2 mile ahead of Car Y --> car X gains 1/2 mile in every 3 minutes (since now it's 1 mile ahead), hence it'll gain additional 1 mile in next 6 minutes. Sufficient.

Hey Guys,

Don't u think that there is a problem in this questions?! How do we know that the cars are moving in the same direction? If they are moving away from each other, then the answer will be completely different, since in (1) the relative speed will be 90 miles/hr, while the answer to (2) remains the same, i.e. 6 minutes.
Notice that the question does not mention that the two cars are travelling in the same direction.
What do you think?
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Re: While on a straight road, Car X and Car Y are traveling at [#permalink]

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02 May 2015, 14:00
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apolo wrote:
Bunuel wrote:
While on a straight road, Car X and Car Y are traveling at different constant rates. If Car X is now 1 mile ahead of Car Y, how many minutes from now will Car X be 2 miles ahead of Car Y ?

(1) Car X is traveling at 50 miles per hour and Car Y is traveling at 40 miles per hour --> since we have the rates of both cars and the distance between them we can calculate any other question regarding them. Sufficient.

(2) Three minutes ago Car X was 1/2 mile ahead of Car Y --> car X gains 1/2 mile in every 3 minutes (since now it's 1 mile ahead), hence it'll gain additional 1 mile in next 6 minutes. Sufficient.

Hey Guys,

Don't u think that there is a problem in this questions?! How do we know that the cars are moving in the same direction? If they are moving away from each other, then the answer will be completely different, since in (1) the relative speed will be 90 miles/hr, while the answer to (2) remains the same, i.e. 6 minutes.
Notice that the question does not mention that the two cars are travelling in the same direction.
What do you think?

Hello apolo

I think when we have words such as "Car A ahead of Car B" or "Car A behind of Car B" is a sign of that they are drive in the same direction.

And when cars driving in different directions there is usually wording such as: "Two cars start off at the same point on a straight highway facing opposite directions."
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Re: While on a straight road, Car X and Car Y are traveling at [#permalink]

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03 May 2015, 08:17
(1) Tells us that car X's relative speed to Y is 10 mph. With this we can easily find the time for X to increase the distance between the two cars with 1 mile. (1mile/10mph*60 minutes/hour=6 minutes)

(2) Tells us that increasing the distance 1/2 mile took 3 minutes. As the speeds in which X and Y are traveling are constant, we can conclude that X will increase the distance with an entire mile in double the time, 6 minutes.
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Re: While on a straight road, Car X and Car Y are traveling at [#permalink]

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21 Mar 2016, 16:45
I didn´t get why 1 is sufficient. We don´t know the directions that the cars are going. If they are at the same direction the differece rate would be 10 mph, but if they are on opposite directions, it would be 90 mph. Could anyone help me?
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Re: While on a straight road, Car X and Car Y are traveling at [#permalink]

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23 Sep 2016, 12:15
Why this is not E ?

The question doesn't mention anything about the direction of the cars.
Re: While on a straight road, Car X and Car Y are traveling at   [#permalink] 23 Sep 2016, 12:15
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