Question 314471: An automobile travels from point A to point B at a speed of 40 km/h. How fast must it travel in the opposite direction to achieve an average speed of 50 km/h for the round trip?
(A) 50 km/h (B) 58 km/h (C) 60 km/h (D) 66• km/h (E) Not enough
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Answer by malaydassharma(59)   (Show Source):
You can put this solution on YOUR website! Let the distance between A and B is 40 Km.
Hence, Total distance covered in journey=40+40=80 Km
Average Speed = 50 Km/hr
Therefore, avg time required for the totaltrip= 80/50= 1 3/5 Hrs
As 1 hr is aleady used during onward journey, remaining time for return journey is 1 3/5 -1 = 3/5 Hrs.for travelling back 40 Kms from B to A.
Hence, Speed = 40 / (3/5)=200/3=66.66 Km/Hr [ Ans(D)]
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