A train travels at an average speed of 90 km/hr without any

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A train travels at an average speed of 90 km/hr without any [#permalink]

27 Apr 2005, 23:53

A train travels at an average speed of 90 km/hr without any stoppages. However, its average speed decrease to 60km/hr on account of stoppages. On an average, how many minutes per hour does the train stop?

(a) 12 minutes
(b) 18 minutes
(c) 24 minutes
(d) 20 minutes
(e) 30 minutes

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28 Apr 2005, 00:28

Distance travelled in 1 hr = 60km
Actual time taken(not including the stops) to cover 60kms = 60/90 hr = 40mins

Therefore, time spent at stops = 20mins.
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28 Apr 2005, 01:52

I think I am making a mistake somewhere, can some one correct me. My solution is as under.

Let d kms be the distance travelled.
Let t hours be the time taken without stoppages.
Let s hours be the total stoppage time.

Putting the above in equations,
d/t = 90 km/hr - (1)
d/(t+s) = 60 km/hr - (2)

Dividing (1) by (2), t/(t+s) = 60/90 (3)

=> s = 30 or the total stoppage time is 30 mins. But this is nowhere in the choice.
Thanks for your help.

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28 Apr 2005, 07:50

this is the way I do it...

speed difference

90-60=30km

30/90*60min=20min

is the additional stoppage time....

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28 Apr 2005, 10:04

t/(t+s) = 60/90

You are right thus far.

Now, read the question again. It says t+s = 60, not t = 60.

That was the only mistake you made.

Once you put t + s = 60 in the above equation, you'll get the right answer.
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28 Apr 2005, 21:06

Thanks for pointing my mistake mckenna. It really helped.

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Re: Average speed of the Train [#permalink]

03 Sep 2011, 08:17

Yayy! I got it right in the first go.
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Re: Average speed of the Train [#permalink] 03 Sep 2011, 08:17

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A train travels at an average speed of 90 km/hr without any

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A train travels at an average speed of 90 km/hr without any

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