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Math Expert V
Joined: 02 Sep 2009
Posts: 53802
Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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Difficulty:   45% (medium)

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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VP  P
Joined: 31 Oct 2013
Posts: 1273
Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)
Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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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.
SVP  P
Joined: 18 Aug 2017
Posts: 2460
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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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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Manager  G
Joined: 01 Feb 2017
Posts: 202
Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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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
Intern  B
Joined: 18 Jan 2019
Posts: 10
Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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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
Manager  G
Joined: 01 Feb 2017
Posts: 202
Re: Distance between two stations A and B is 778 km. A train covers the jo  [#permalink]

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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.

Posted from my mobile device 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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# Distance between two stations A and B is 778 km. A train covers the jo

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