Aptitude - Problems on Trains - Discussion

Your running at a speed of 5km/hr
(1km=1000 meter and 1hr=3600seconds,which will be 1000/3600=10/36=5/18)
Note :for 1 km/hr
Therefore 5(given km)*5/18=1.39
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Meanwhile 125m long train crosses you in 10 seconds along with you in same diretion.
Then!!
125/10 i.e its in the form of (125)m/(10)s.
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So add those two values in the form of m/s,which is 13.89=a
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Now question to find speed of the train,since we found in the form of m/s,but the options provided are in the form of KM/HR
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So to convert M/S to KM/HR :
(a*18/5)=(13.89*3.6)
Gives answer as 50 km/hr

How/ why Let the speed of the train be x km/hr. Then, relative speed = (x - 5) km/hr.

Please any one explain me why let speed =(x-5)km hr.

It is brain storming and conceptual question .Thank you for giving more explanation on this question.Thank you very much....!

125/10 = 25/2

25/2*18/5 = 450/10
45

friends,
i don't know how to solve this problems after this
so plz anyone help me out

Just try this 1 sec 5 km/hr means 10 sec is 50 km/hr thats it..
becoz the man running at same time train is moving ..

Abisheks answer is realy nice. Thank you abi.

To convert km/h into m/s we multiply that value with 5/18.why is this because
1km=1000m
1h=60min*60sec=3600sec
now
1km/h=1000/3600=5/18
if we want to convert m/s into km/h we have to multiply with 18/5.
hope you can understand.

x-5 is nothing but here x refers to the speed of train and as both train and boy are moving in the same direction relative velocity comes into picture and here relative velocity is the difference of two velocities.

If train moving same direction = SUBTRACTION OCCUR.
If train moving opposite direction = ADDITION OCCUR.

Let the speed of the train is x km/hr
Then the relative speed is (x-5)km/hr
Therefore,
Time = 10sec
Distance = 125m
Speed = (x-5)km/hr
As we are calculating in m/sec so we have to convert km/hr to m/sec.
(x-5)*1000/3600 m/sec or (x-5)*5/18 {by cancelling by 200.
200*5=1000,200*18=3600}

Therefore ,

Speed = distance/ time
(x-5)5/18 = 125/10
x-5 = 125*18/10*5
x-5 = 2250/50
x-5 = 45
x = 45+5
x = 50
Therefore x is 50km/hr (speed of the train)