A fun Questions about trains

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A fun Questions about trains
Jun 21, 2011 08:03
guest12982	Train A leaves from Shanghai to Nanjing at 7am, at a speed of 100 km/h on one track. Train B leaves Nanjing to Shanghai also at 7 am, at a speed of 250 km/h on parallel track. Now the question: when they pass/cross each other, somewhere along the line, which one will be closer to Shanghai?

Jun 21, 2011 21:03	#1
LINGYUXISU Points: Join Date: Dec 3, 2010 Status: Offline	How long is this railway line between Nanjing and Shanghai?

Jun 21, 2011 21:41	#2
GUEST12982	I actually measured it: it's 303 km.

Jun 22, 2011 03:24

LINGYUXISU
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The past time (used time) is unknown when the two trains meet, so let's assume it an X.
So we could calculate it this way: 100X + 250X = 303, so X=303/350, right?
Then the Train A leaving from Shanghai will go this long when they meet, 303/350x100, which means it is 303/350x100 kilometers away from shanghai.
Train B leaving from Nanjing will go this long when they meet: 303/350x250 and it is 303-303/350x250 kilometers away from Shanghai.
You just compare to see which one is closer to Shanghai.

Am I right?

Jun 22, 2011 04:05	#4
GUEST12982	sorry, you are incorrect.

Jun 22, 2011 04:10	#5
LINGYUXISU Points: Join Date: Dec 3, 2010 Status: Offline	Then how do you solve this math problem?

Jun 22, 2011 09:35

ATTA_BUTT
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Train A leaves from Shanghai to Nanjing at 7am, at a speed of 100 km/h on one track.
Total actually measured distance 303 KM
So it got distance 303-100=203 KM. after one hour.
So closer to Shanghai 303-203= 100 KM.

Train B leaves from Nanjing to Shanghai at 7am, at a speed of 250 km/h on one track.
Total actually measured distance 303 KM
So it got distance 303-250=53 KM. At one hours.

Train A is away from Shanghai only 100 KM. After one hour

Train B is away from Shanghai only 53 KM. After one hour

Jun 22, 2011 14:41

CARLOS
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When they pass each other them both are in same place. There is only one but: do we measure from the front or back of train? If front, then the distance from Shanghai is same, if back, the back of train A is closer to Shanghai.

To question when do they pass:

x100 km/h+x250 km/h = 303 km where x is time in hours
next
350x = 303
and then time from start to passing
303/350 = 52min
Time for passing is 07:52

Train A travels about 86,5 km in 52 min, train B about 216,5 km. 86,5+216,5 = 303km.
The passing place is around Kuatangzhen

Carlos

Jun 22, 2011 20:50	#8
GUEST12982	Bravo Carlos! When they pass each other, both front ends of train A and train B will be in the same place, so at that split second they are both as close as to Shanghai...or Nanjing (my two favorite cities).

Jun 23, 2011 01:57	#9
GUEST1657	I HATE math problem because I was punished by my math teacher many times in primary school. You know why? He let us do many math problems like the above one.

Jun 23, 2011 03:21	#10
LINGYUXISU Points: Join Date: Dec 3, 2010 Status: Offline	Quote: Originally Posted by GUEST12982 Bravo Carlos! When they pass each other, both front ends of train A and train B will be in the same place, so at that split second they are both as close as to Shanghai...or Nanjing (my two favorite cities). Got it, Thank you. It was interesting.

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