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26 Feb 2016, 06:24
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Andrew drove from A to B at 60 miles per hour. Then he realized that he forgot something at A, and drove back at 80 miles per hour. He then zipped back to B at 90 mph. What was his approximate average speed in miles per hour for the entire night?
Culled from M-GMAT word translation guide.
Is there any concise way of solving this problem?
Cos the solution given by M-gmat wasn't a CAT-wise solution, IMO. Twas quite long considering the nature of the question.
I'll appreciate with kudos any solution that didn't draw up a big table.
Official answer was given as 74.5. No options were given.
Culled from M-GMAT word translation guide.
Is there any concise way of solving this problem?
Cos the solution given by M-gmat wasn't a CAT-wise solution, IMO. Twas quite long considering the nature of the question.
I'll appreciate with kudos any solution that didn't draw up a big table.
Official answer was given as 74.5. No options were given.
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Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Problem Solving (PS) Forum
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26 Feb 2016, 06:36
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Andrew drove from A to B at 60 miles per hour. Then he realized that he forgot something at A, and drove back at 80 miles per hour. He then zipped back to B at 90 mph. What was his approximate average speed in miles per hour for the entire night?
Culled from M-GMAT word translation guide.
Is there any concise way of solving this problem?
Cos the solution given by M-gmat wasn't a CAT-wise solution, IMO. Twas quite long considering the nature of the question.
I'll appreciate with kudos any solution that didn't draw up a big table.
Official answer was given as 74.5. No options were given.
Culled from M-GMAT word translation guide.
Is there any concise way of solving this problem?
Cos the solution given by M-gmat wasn't a CAT-wise solution, IMO. Twas quite long considering the nature of the question.
I'll appreciate with kudos any solution that didn't draw up a big table.
Official answer was given as 74.5. No options were given.
All average speed questions are dealt in the same way.
\(Average Speed = \frac {Total distance} { Total Time taken}\)
Total distance = A to B + B to A+ A to B = S+S+S=3S
Total time = S/60 + S/80+S/90
Thus, \(Average speed = \frac{3S}{S/60 + S/80+S/90}\), after cancelling out the S from the Numerator and the Denominator, you are left with,
\(Average speed = \frac{30}{29/72} = \frac {30*72}{29}\), now realize that 30/29 is just >1 and thus the average speed = just more than 72 mph.
Actual value : \(Average speed = \frac{30}{29/72} = 74.48 mph\)
Hope this helps.
P.s.: IMO, you dont need the fancy tables or methods if you know what you are dealing with.
20 Apr 2017, 10:42
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Just picked LCM of 60,80 and 90 = 720
Calculated total time in each session = 29
Avg speed = 720*3/29= 74.48
Calculated total time in each session = 29
Avg speed = 720*3/29= 74.48
Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Problem Solving (PS) Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
