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A car traveling at a certain constant speed takes 2 seconds

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A car traveling at a certain constant speed takes 2 seconds [#permalink] New post 28 Jan 2012, 03:10
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A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5
B. 72
C. 72.5
D. 73
E. 73.5
[Reveal] Spoiler: OA

Last edited by Bunuel on 28 Jan 2012, 03:59, edited 1 time in total.
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Re: Rate [#permalink] New post 28 Jan 2012, 03:58
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RadhaKrishnan wrote:
A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5
B. 72
C. 72.5
D. 73
E. 73.5


Many approaches are possible, one of them:

Let the distance be 1 kilometer.

Time to cover this distance at 75 kilometers per hour is 1/75 hours = 3,600/75 seconds = 48 seconds;
Time to cover this distance at regular speed is 48+2=50 seconds = 50/3,600 hours = 1/72 hours;
So, we get that to cover 1 kilometer 1/72 hours is needed --> regular speed 72 kilometers per hour (rate is a reciprocal of time or rate=distance/time).

Answer: B.
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Re: A car traveling at a certain constant speed takes 2 seconds [#permalink] New post 30 Jan 2012, 00:11
if 1 h=60*60 sec, then 2 sec =2/60*60=1/1800

1/1800+1/75=25/1800=1/72

since t=D/S and t=1/72 D=1 then S=72
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Re: A car traveling at a certain constant speed takes 2 seconds [#permalink] New post 30 Jan 2012, 02:41
B - 72

Original time in seconds: 60*60/75 = 48 --> Car need 48 seconds to travel 1 km
New car needs 2 more seconds to travel 1km --> 50 seconds to travel 1km

Speed (new car): 50 (seconds) / 3600 (1 hour in seconds) = 1 / 72 --> in 1 Minute the car travels 1 / 72. Thus 72km/h
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Re: A car traveling at a certain constant speed takes 2 seconds [#permalink] New post 27 Nov 2014, 13:50
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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Re: A car traveling at a certain constant speed takes 2 seconds [#permalink] New post 27 Jan 2015, 02:24
Bunuel wrote:
RadhaKrishnan wrote:
A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5
B. 72
C. 72.5
D. 73
E. 73.5


Many approaches are possible, one of them:

Let the distance be 1 kilometer.

Time to cover this distance at 75 kilometers per hour is 1/75 hours = 3,600/75 seconds = 48 seconds;
Time to cover this distance at regular speed is 48+2=50 seconds = 50/3,600 hours = 1/72 hours;
So, we get that to cover 1 kilometer 1/72 hours is needed --> regular speed 72 kilometers per hour (rate is a reciprocal of time or rate=distance/time).

Answer: B.


Dear BUnuel,

Do you confirm this approach?

75 km is 75000 m and 1 hour is 60 min. so we have : 1000*60 /75000 = 4/5 min OR 4/5 *60 = 48 seconds
AS the promblem says take 2 seconds longer so we have 48+2 =50 seconds to cover 1 km or 1000 m
as we have formula like this: V*t = d so we have v*50= 1000 Or v= 1000/50 = 20 m/s

NOW convert to Km/h : 20 * 3600 (s) /1000 m = 72000/1000 = 72 km/h

Please confirm if this is true
Thanks :lol:
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Re: A car traveling at a certain constant speed takes 2 seconds [#permalink] New post 04 Feb 2015, 05:02
mehrdadtaheri92 wrote:
Bunuel wrote:
RadhaKrishnan wrote:
A car traveling at a certain constant speed takes 2 seconds longer to travel 1 kilometer than it would take to travel 1 kilometer at 75 kilometers per hour. At what speed, in kilometers per hour, is the car traveling?

A. 71.5
B. 72
C. 72.5
D. 73
E. 73.5


Many approaches are possible, one of them:

Let the distance be 1 kilometer.

Time to cover this distance at 75 kilometers per hour is 1/75 hours = 3,600/75 seconds = 48 seconds;
Time to cover this distance at regular speed is 48+2=50 seconds = 50/3,600 hours = 1/72 hours;
So, we get that to cover 1 kilometer 1/72 hours is needed --> regular speed 72 kilometers per hour (rate is a reciprocal of time or rate=distance/time).

Answer: B.


Dear BUnuel,

Do you confirm this approach?

75 km is 75000 m and 1 hour is 60 min. so we have : 1000*60 /75000 = 4/5 min OR 4/5 *60 = 48 seconds
AS the promblem says take 2 seconds longer so we have 48+2 =50 seconds to cover 1 km or 1000 m
as we have formula like this: V*t = d so we have v*50= 1000 Or v= 1000/50 = 20 m/s

NOW convert to Km/h : 20 * 3600 (s) /1000 m = 72000/1000 = 72 km/h

Please confirm if this is true
Thanks :lol:


I'm not Bunuel but I don't see anything wrong in the approach.
Re: A car traveling at a certain constant speed takes 2 seconds   [#permalink] 04 Feb 2015, 05:02
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