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Re: A train travels at an average speed of 90 km/hr without any stoppages. [#permalink]
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Actual Speed of the train = 90 KM/Hr = 1.5 KM / Min
Distance Travelled = 60 KM, Speed = 1.5 Km / Min, hence time = 60/1.5=>40 Mins

Halt Minutes = 60 - 40 =>20 Mins
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Re: A train travels at an average speed of 90 km/hr without any stoppages. [#permalink]
Don't we need to assume for that answer that we can ignore the deceleration of the train when arriving at a stop?
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A train travels at an average speed of 90 km/hr without any stoppages. [#permalink]
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Let's say the distance the train travels is D kilometers. Thus, with stoppages it takes D/60 hrs and without stoppages it would have taken D/90 hrs. So for a D/60 hour trip, the train loses D/180 hrs (D/60 - D/90). Therefore, the time lost PER HOUR due to stoppages is:
(D/180)/(D/60)=1/3 hrs=20 minutes. Ans: C
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Re: A train travels at an average speed of 90 km/hr without any stoppages. [#permalink]
Bunuel, can you please confirm the below thought process?

Avg Speed (w/ stops) = Distance / Total Time = 60 km/hr

Distance = (90 km/hr)(t1 hr) + (0 km/hr)(t2 hr) (km)
Total Time = t1 + t2 (hr)

Solve to get
t1/t2 = 2hr/1hr

In order to Avg 60 km/hr you need 2 hrs of 90 km/hr for every 1 hour the train is stopped (0 km/hr)
OR
1/3 of every hour = 20 minutes stopped C, 40 minutes running at 90 km/hr
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Re: A train travels at an average speed of 90 km/hr without any stoppages. [#permalink]
effatara wrote:
Let's say the distance the train travels is D kilometers. Thus, with stoppages it takes D/60 hrs and without stoppages it would have taken D/90 hrs. So for a D/60 hour trip, the train loses D/180 hrs (D/60 - D/90). Therefore, the time lost PER HOUR due to stoppages is:
(D/180)/(D/60)=1/3 hrs=20 minutes. Ans: C


can you explain the reasoning behind (D/180)/(D/60) ??

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

(A) 12 minutes
(B) 18 minutes
(C) 20 minutes
(D) 24 minutes
(E) 30 minutes


In 1 hour, the train travels 90 km (if there are no stoppages).
But in 1 hour, it actually travels only 60 km i.e. 2/3rd of the distance. So actually it runs for only 2/3rd the time i.e. 40 mins. So it stops for 20 min per hour on average.
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Re: A train travels at an average speed of 90 km/hr without any stoppages. [#permalink]
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Re: A train travels at an average speed of 90 km/hr without any stoppages. [#permalink]
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