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What if the the position man is standing is not a point but rather say .004 meters(may be a real fat one)
in that case it would
Distance travelled by train to cross the man = 18 * 20 = 360 = Distance occupied by man in platform + Length of train
The answer has to be E
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raarun
What if the the position man is standing is not a point but rather say .004 meters(may be a real fat one)
in that case it would
Distance travelled by train to cross the man = 18 * 20 = 360 = Distance occupied by man in platform + Length of train
The answer has to be E

I do not think that we have to go into such minute detail and include the length of the person's waist as its negligible when compared to the overall length.
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raarun
What if the the position man is standing is not a point but rather say .004 meters(may be a real fat one)
in that case it would
Distance travelled by train to cross the man = 18 * 20 = 360 = Distance occupied by man in platform + Length of train
The answer has to be E

hi,
Vyshak is correct..
Don't complicate the Q, where it is not required..
If you want to have E as the answer, you don't require a fat person of .004m, even a thin guy of .001m will also effect the distance by that small amount..
But that is not required, we take the person as a point.
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Why do we have to subtract 18*20 from 30*20?

I don´t really get the connection between the two numbers.
Maybe someone can explain how the fact that the train needs 18 seconds to pass the person is related to the length of the platform?
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first find length of train:
18 s=1/200 h
72 kh*1/200 h=9/25 k=length of train
next find length of platform (p):
30 s=1/120 h
72 kh*1/120 h=9/25 k+p
p=6/25 k=240 m
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\(Well\; this\; was\; fun.\)

\(We\; have\; to\; take\; into\; consideration\; the\; lenght\; of\; the\; train\; in\; this\; problem,\;\)
\(considering\; the\; time\; it\; takes\; the\; head\; of\; the\; train\;\)
\(to\; go\; from\; the\; start\; of\; the\; platform\; to\; the\; end\; of\; it.\;\)

\(\mbox{S}o\; if\; it\; takes\; take\; train\; 18\; seconds\; to\; pass\; a\; standing\; man,\;\)
\(it\; means\; that\; the\; lenght\; of\; the\; train\; was\; 72*\frac{1000}{3600}\; =\; 20\; *\; 18\; ->\; 360\; metres.\)

\(Found\; the\; lenght\; we\; simply\; need\; to\; do\; 20*30\; ->\; 600\;\)
\(which\; is\; the\; time\; the\; train\; takes\; to\; completely\; leave\; the\; platform\;\)

\(and\; subtract\; the\; lenght\; of\; the\; train:\; 600-360\; =\; 240\)

\(Answer\; A.\)
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In speed-distance questions, always remember-
Pole, a man (stationary) etc are considered as points, when a train crosses these, it means that the train travelled a distance equal to its own length.
while,
Other trains, railway platform etc are considered for their own lengths, it means that if a moving train crosses these, the train travelled a distance equal to its own length + length of the other train/platform

Coming to this question:
Speed of the train: 72 km/h = \(72*\frac{5}{18}\) = 20 meters/sec ----(converting into mt/sec as everything else is in meters and seconds)

Train crosses a man (a stationary point) in 18 secs: Train covers its own length in 18 secs:
Length of train = \(20 * 18 = 360\) meters

Train crosses a platform in 30 secs: Train covers a distance equal to its own length+length of the platform in 30 secs:
i.e. length of the train + Length of the platform = 20 * 30 ----(Distance = Speed * Time)
\(360+x = 600\)
\(x = 240\)

Length of the platform = 240 meters

A
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Bunuel
A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 18 seconds. What is the length of the platform in meters?

A. 240 meters
B. 360 meters
C. 420 meters
D. 600 meters
E. Cannot be determined

We can let p = the length of the platform, in meters, and t = the length of the train, in meters.

When we say the train crosses a platform in 30 seconds, it really means it takes 30 seconds for the nose of the train to enter one end of the platform and the rear of the train to exit the other end of the platform. Thus, in 30 seconds, not only does the train’s nose travel the entire length of the platform but also its entire body length does. Thus, we have (notice that 72 kmph = 72000 meters per hour, and 30 sec = 30/3600 = 1/120 hr):

72000 x 1/120 = p + t

600 = p + t

p = 600 - t

We are also given that the train crosses a man (whose body width is negligible) standing on the platform in 18 seconds. So when the train crosses him, it only travels its body length in 18 seconds. Thus we have (notice that 18 sec = 18/3600 = 1/200 hr):

72000 x 1/200 = t

360 = t

Therefore, the platform has a length of 600 - 360 = 240 meters.

Answer: A
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A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 18 seconds. What is the length of the platform in meters?

A. 240 meters
B. 360 meters
C. 420 meters
D. 600 meters
E. Cannot be determined

Step 1:
To cross the platform = 72 km/h = 72 km/60 minutes = 1.2 km/60 seconds = 0.6 km/30 seconds = 600 meters

Step 2:
To cross the man = 72 km/h = 72 km/60 minutes = 1200 meter/60 seconds , 18 seconds =360 Meters

Step 3:
Length of platform = 600 - 360 = 240

Ans: A
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Hi Brent GMATPrepNow

This explanation is elegant and magnificent. Thanks for you effort :thumbup:
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Hi Brent GMATPrepNow

This explanation is elegant and magnificent. Thanks for you effort :thumbup:

Thanks for taking the time to say that!

Cheers,
Brent
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A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 18 seconds. What is the length of the platform in meters?

A. 240 meters
B. 360 meters
C. 420 meters
D. 600 meters
E. Cannot be determined
Given that, the speed of train = 72 kmph = 72(5/18) msec
= 20 msec
(The distance of train )/(Speed of train) = time
x/20 = 18
X = 260
In case of crossing platform,
(The distance of train+The distance of Platform )/(Speed of train) = Time
(y+360)/20 = 30
Y + 360 = 600
Y = 240(A)
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72 kmph = (72,000 meters) / (3,600 seconds) = 20 met/sec


To entirely cross the platform, the train has to cover its own length(L) plus the length of the platform (P)

In 30 seconds traveling at 20 met/sec ——— train can cover distance of ( L + P) meters

(20) (30) = L + P


To cross the man, all the train has to do is put its own length (L) in front of the man. Since the train does this in 18 seconds at the same speed

(20) (18) = L


Subtract the 2nd equation from the 1st equation



P = (30) (20) - (20) (18)

P = (20) (30 - 18)

P = 20 * 12 = 240 meters

A

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Difference between time = 30-18 = 12 sec= Time required to pass distance equals to Platform

As Speed = Distance /Time or, Distance = 72* \(\frac{12}{(60*60)}\) = 0.24 Km

So, I think A. :)
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Given: A train traveling at 72 kmph crosses a platform in 30 seconds and a man standing on the platform in 18 seconds.
Asked: What is the length of the platform in meters?

72kmph = 72*1000/60*60 = 20 m/s

Length of the train = 20 * 18 = 360 m
Length of the train + Length of the platform = 20 * 30 = 600 m
Length of the platform = 600 - 360 = 240 m

IMO A
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