Latest CDS Aptitude Question SOLUTION: a train travels a distance of 300km at a constant speed.if the speed of the train is increased by 5km/hr,the journey would have taken two hours less.find the initial speed of the t

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a train travels a distance of 300km at a constant speed.if the speed of the train is increased by 5km/hr,the journey would have taken two hours less.find the initial speed of the train?

Asked In CDS godwin (12 years ago)

Solved jyotish r Read Solution (5)

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chaitanya  (12 years ago)

we know that, s = d / t
distance = 300 km
initail speed ( s) , new speed = s + 5
initial time taken ( t ) = 300 / s and new time taken = 300 / s + 5
so now, according to the ques :
300 / s + 5 + 2 = 300 / s
2 = 300 / s + 300 / s + 5
2 = (300s + 1500 - 300s) / s 2 + 5s
2s 2 + 10s - 1500 = 0
s 2 + 5s + 750 = 0
s2 - 25s + 30s - 750 = 0
s ( s - 25) + 30 ( s - 25 ) = 0
s = 25 or -30

answer: 25 km / hr..

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Arun  (12 years ago)

Let the speed of the train be "x km/hr"
so time=distance/speed
=>time=300/x
now if we will increse the speed of train,then it will take 2hr less.
new speed =x+5
SO comparing time we can form equation as
(300/x)-(300/x+5)=2
Solving the equation x=25 (As we will take the positive calue of x)

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jyotish r  (12 years ago)

let the speed=x km/hr
time to travel 300km=300/x hr
at a speed of x+5km/hr=300/(x+5) hr
300/x - 300/(x+5) = 2
(x+30)*(x-25)=0
x=25 is the answer(x=-30 not possible since x should be positive )

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aanchal sharma  (12 years ago)

let x1 be the initial speed of train,
x1=300/t1
and x2 be the increased speed , x2 = (x+5)=(300/t1 + 5)
x1*t1=x2*t2(if distance is same then s1*t1=s2*t2)
(300/t1)*t1=(300/t+5)(t1-2)
this gives t1 = 10hrs
x1=300/10
x1=30km/hr.

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ritesh kumar pandey  (11 years ago)

25 km/hr

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