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

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Senior Manager
Joined: 15 Apr 2005
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Location: India, Chennai
A train travels at an average speed of 90 km/hr without any [#permalink]

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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

Thanks

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Manager
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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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Anyone who has never made a mistake has never tried anything new. -Albert Einstein.

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Senior Manager
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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.

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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

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Manager
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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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Anyone who has never made a mistake has never tried anything new. -Albert Einstein.

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Senior Manager
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28 Apr 2005, 21:06
Thanks for pointing my mistake mckenna. It really helped.

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Senior Manager
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Re: Average speed of the Train [#permalink]

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03 Sep 2011, 08:17
Yayy! I got it right in the first go.
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petrifiedbutstanding

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Re: Average speed of the Train   [#permalink] 03 Sep 2011, 08:17
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