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Distance between two stations A and B is 778 km. A train covers the jo

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Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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New post 21 Feb 2019, 00:20
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Question Stats:

64% (02:34) correct 36% (02:33) wrong based on 45 sessions

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Distance between two stations A and B is 778 km. A train covers the journey from A to B at 84 km per hour and returns back to A with a uniform speed of 56km per hour. Find the average speed of the train during the whole

A. 66.5 km/hr
B. 67.2 km/hr
C. 67.7 km/hr
D. 68.6 km/hr
D. 68.9 km/hr

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Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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New post 21 Feb 2019, 02:28
Bunuel wrote:
Distance between two stations A and B is 778 km. A train covers the journey from A to B at 84 km per hour and returns back to A with a uniform speed of 56km per hour. Find the average speed of the train during the whole

A. 66.5 km/hr
B. 67.2 km/hr
C. 67.7 km/hr
D. 68.6 km/hr
D. 68.9 km/hr



Average speed :

2xy / x + y

= 2* 84 * 56 / 140

= 67.2.

B is the correct answer.
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Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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New post 21 Feb 2019, 08:28
Bunuel wrote:
Distance between two stations A and B is 778 km. A train covers the journey from A to B at 84 km per hour and returns back to A with a uniform speed of 56km per hour. Find the average speed of the train during the whole

A. 66.5 km/hr
B. 67.2 km/hr
C. 67.7 km/hr
D. 68.6 km/hr
D. 68.9 km/hr


use avg speed formula ; since distance is same

2*ab/a+b
; 2 * 84*56/140
IMO B 67.2 km/hr
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Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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New post 27 Feb 2019, 10:42
As distance for either leg is same i.e 778 km, average speed is not dependent on actual distance.
For ease of calculations, assume distance between A-B as 1.

Time A-B: 1/84
Time B-A: 1/56
Time total: 1/84 + 1/56= 140/84*56= 5/84*2
Total distance: 2
Avg Spd: total distance / total time: 2*84*2/5 = 84*8/10= 672/10= 67.2
Ans B
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Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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New post 03 Mar 2019, 08:51
Shobhit7 wrote:
As distance for either leg is same i.e 778 km, average speed is not dependent on actual distance.
For ease of calculations, assume distance between A-B as 1.

Time A-B: 1/84
Time B-A: 1/56
Time total: 1/84 + 1/56= 140/84*56= 5/84*2
Total distance: 2
Avg Spd: total distance / total time: 2*84*2/5 = 84*8/10= 672/10= 67.2
Ans B


I understand logically that average speed is not dependent on distance since it is the same on both legs, however, why does this mean you can equate it to 1? Can you please explain this
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Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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New post 03 Mar 2019, 08:58
Ish1996 wrote:
Shobhit7 wrote:
As distance for either leg is same i.e 778 km, average speed is not dependent on actual distance.
For ease of calculations, assume distance between A-B as 1.

Time A-B: 1/84
Time B-A: 1/56
Time total: 1/84 + 1/56= 140/84*56= 5/84*2
Total distance: 2
Avg Spd: total distance / total time: 2*84*2/5 = 84*8/10= 672/10= 67.2
Ans B


I understand logically that average speed is not dependent on distance since it is the same on both legs, however, why does this mean you can equate it to 1? Can you please explain this


Just to ease off the calculation.

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Re: Distance between two stations A and B is 778 km. A train covers the jo   [#permalink] 03 Mar 2019, 08:58
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