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To travel 600 Km

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by neoreaves » Wed Apr 28, 2010 10:20 am
To travel 600 Km , train x takes 8 hours more than train y. If however, the speed of the train x is doubled, it takes 2 hours less than train y. What is the speed of the train y?


sorry guys don't have the answer choices ...i know its a hassle without them but just wanna confirm my answer
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by rn4gmat » Wed Apr 28, 2010 10:29 am
There would be two equations like :

600/x -600/y = 8

And 600/y - 600/2x = 2

this can be equated to 600 = 20x

So the value of x is : 30 km/hr

putting this is euation one we get : 600/30 -8 = 600/y => y = 50 km/hr


Hope this helps.
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by sandeepkar » Wed Apr 28, 2010 11:48 am
Time to travel 600 miles for Train Y = t
Time to travel 600 miles for Train X = t+8
Train X Speed = 600/(t+8)

Time to travel 600 miles for Train X if speed is doubled = t-2

distance traveled by train X with double speed = speed*time = [2*(600/(t+8))]*(t-2)

[2*(600/(t+8))]*(t-2) = 600

so t= 12

Train Y Speed = 600/t = 600/12 = 50
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by harshavardhanc » Thu Apr 29, 2010 1:07 am
neoreaves wrote:To travel 600 Km , train x takes 8 hours more than train y. If however, the speed of the train x is doubled, it takes 2 hours less than train y. What is the speed of the train y?


sorry guys don't have the answer choices ...i know its a hassle without them but just wanna confirm my answer
want to avoid equations?

here's one method.

you know that distance remaining constant, speed is inversely proportional to time. i.e

if speed is doubled the time becomes half of the previous value.

now this 50% decrease in time is given to be 10 hours (8+2). => 100% of the time of x will be 20 hours.

which tells us that Y takes 8 hours less i.e 12 hours. Hence, speed of y =600/12 = 50 ;)
Regards,
Harsha
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