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
Could you please explan using RTD chart. Thansk a lot!
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k_abhi19
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The answer is B... a simpler approach can be to think it like this...
when travelling at 75kmph.. the car travels 1 km in 48 secs (as 1/75 hrs or 3600/75=48 secs) and thus we need to find out the speed when car travels 1 km in 50 (48 + 2) secs.... now 50 secs is nothing but 1/72 hr (3600 secs = 1hrs i.e 50 secs = 1/72 hrs).. thus speed will be Dist/time i.e 1/(1/72) kmph.. or 72kmph...
when travelling at 75kmph.. the car travels 1 km in 48 secs (as 1/75 hrs or 3600/75=48 secs) and thus we need to find out the speed when car travels 1 km in 50 (48 + 2) secs.... now 50 secs is nothing but 1/72 hr (3600 secs = 1hrs i.e 50 secs = 1/72 hrs).. thus speed will be Dist/time i.e 1/(1/72) kmph.. or 72kmph...
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gixxer1000
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I did it the tradition way but it will probably take longer.
R*T=D, So:
75km/hr * T = 1km
T = 1/75hr
Then add two seconds, but first convert it two hrs
2sec * 1min/60sec * 1hr/60min = 1/1800hr
1/75hr + 1/1800hr = 1875/135000
Simplify
1/72hr
Now use this time to solve for the rate:
R * 1/72hr = 1km
R = 72km/hr
R*T=D, So:
75km/hr * T = 1km
T = 1/75hr
Then add two seconds, but first convert it two hrs
2sec * 1min/60sec * 1hr/60min = 1/1800hr
1/75hr + 1/1800hr = 1875/135000
Simplify
1/72hr
Now use this time to solve for the rate:
R * 1/72hr = 1km
R = 72km/hr
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rahul.s
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75 kms 3600 seconds
1 km ? seconds
3600/75 = 48 seconds to cover a distance of 1 km.
Now, we have to find the speed of the car per hour that takes 50 seconds to cover a distance of 1 km
50 seconds 1 km
3600 seconds ? kms
3600/50 = 72
So, it's B
1 km ? seconds
3600/75 = 48 seconds to cover a distance of 1 km.
Now, we have to find the speed of the car per hour that takes 50 seconds to cover a distance of 1 km
50 seconds 1 km
3600 seconds ? kms
3600/50 = 72
So, it's B
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mcdesty
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My scratch paper looked like this when I tackled this one.
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Hi All,
It looks like most of the users in this post are long gone (2008 to 2010), but for anyone who might be interested, there are other ways to "do the math" in this prompt:
75 kilometers per hour is the same as 75 kilometers per 60 minutes....
75/60 = 5/4 = 5 kilometers every 4 minutes
This means that every 1 kilometer takes 4/5 minutes = 48 seconds
We're then asked to add 2 seconds to this and calculate the speed.
48 + 2 = 50 seconds
To find the speed, we can use a ratio (50 seconds = 5/6 minutes):
5/6 = 60 min/X kph
Cross multiply the ratio:
5X = 360
X = 72 kph
Final Answer: B
GMAT assassins aren't born, they're made,
Rich
It looks like most of the users in this post are long gone (2008 to 2010), but for anyone who might be interested, there are other ways to "do the math" in this prompt:
75 kilometers per hour is the same as 75 kilometers per 60 minutes....
75/60 = 5/4 = 5 kilometers every 4 minutes
This means that every 1 kilometer takes 4/5 minutes = 48 seconds
We're then asked to add 2 seconds to this and calculate the speed.
48 + 2 = 50 seconds
To find the speed, we can use a ratio (50 seconds = 5/6 minutes):
5/6 = 60 min/X kph
Cross multiply the ratio:
5X = 360
X = 72 kph
Final Answer: B
GMAT assassins aren't born, they're made,
Rich
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If 1 kilometer requires 2 more seconds, then 75 kilometers requires 150 more seconds.beater 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
Implication:
The rate of the car =
= (75 kilometers)/(1 hour + 150 seconds)
= (75 kilometers)/(3750 seconds)
= 1 kilometer/50 seconds
= 2 kilometers/100 seconds
= 72 kilometers/3600 seconds
= 72 kilometers per hour.
The correct answer is B.
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abhasjha
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few things that come handy before you proceed to solve the problem :
(1) zkm/hr = z(5/18) m/s ... ( use conversion 1 km= 1000m ;an hour = 3600 seconds)
(2) zmeter/second = z(18/5) km/hour .
now on to the question
75 kilometers per hour= 75(5/18)m/second
distance = 1 km = 1000m
thefore time taken in this case = distance / speed. 1000/(75x5)/18 = 48 seconds
A car traveling at a certain constant speed takes 2 seconds longer . therefore actual time taken = 48+2= 50 seconds .
distance = 1 kilometer .
so speed = (1000meter) /50 . = 20meter/s
converting 20m/s imto km/hr = 20x18/5 = 72km/hr.
so answer B.
(1) zkm/hr = z(5/18) m/s ... ( use conversion 1 km= 1000m ;an hour = 3600 seconds)
(2) zmeter/second = z(18/5) km/hour .
now on to the question
75 kilometers per hour= 75(5/18)m/second
distance = 1 km = 1000m
thefore time taken in this case = distance / speed. 1000/(75x5)/18 = 48 seconds
A car traveling at a certain constant speed takes 2 seconds longer . therefore actual time taken = 48+2= 50 seconds .
distance = 1 kilometer .
so speed = (1000meter) /50 . = 20meter/s
converting 20m/s imto km/hr = 20x18/5 = 72km/hr.
so answer B.
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If Speed of Car = Sbeater 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
Could you please explan using RTD chart. Thansk a lot!
TIME = DISTANCE / SPEED
TIME to travel 1 KM at 75 KMPH = 1/75 Hour = 3600/75 Sec [Because 1 Hour = 3600 Secs]
TIME to travel 1 KM at S KMPH = 1/S Hour = 3600/S Sec
Given, (3600/S) - (3600/75) = 2 Seconds
i.e. (3600/S) - 48 = 2 Seconds
i.e. (3600/S) = 50 Seconds
i.e. S = 72 KM/HOUR
Answer: Option B
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We can let r = the speed of the car in km per hour; thus it would take the car 1/r hour to travel 1 km. If the car traveled at 75 km per hour, then it would take the car 1/75 hour to travel 1 km.beater 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
We are given that the car would be 2 seconds faster traveling 1 km had it traveled at 75 km per hour. Since 2 sec = 1/1800 hour, we can create the following equation:
1/75 + 1/1800 = 1/r
Multiplying the entire equation by 1800r, we have:
24r + r = 1800
25r = 1800
r = 72
Answer: B
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Brent@GMATPrepNow
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Let's start with a word equation.beater 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
GIVEN: 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.
Let x = the car's speed
We can write: (travel time at x km per hour) = (travel time at 75 km per hour) + 2 seconds
Since the speeds are in km per HOUR, let's rewrite 2 seconds as 2/3600 hours (since there are 3600 second in one hour)
We get: (travel time at x km per hour) = (travel time at 75 km per hour) + 2/3600 hours
Or: (travel time at x km per hour) = (travel time at 75 km per hour) + 1/1800 hours
Travel time = distance/spee
We get: 1/x = 1/75 + 1/1800 hours
The least common multiple of the denominators is 1800x, so....
Multiply both sides by 1800x to get: 1800 = 24x + x
Simplify: 1800 = 25x
Solve: x = 1800/25 = 72
Answer: B
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