The Mystifying Round Trip

Classical Mechanics Level pending

John traveled from New York to Boston at an average speed of 60 mph. On the trip back, he averaged 40 mph.

What was John's average speed for the two trips in mph?


The answer is 48.

John Zack by John Zack , 27, Philippines

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2 solutions

Mardokay Mosazghi
Jun 28, 2014

I am not going to explain the conceptional part as John Zack did but the math part in getting the answer can be done easily by ( 60 ∗ 40 ) / ( 60 + 40 ) ∗ 2 = 48 (60*40)/(60+40) *2 =48

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John Zack
May 14, 2014

This problem's quite tricky, so simply averaging 60 mph and 40 mph to get 50 won't do.

First, you need a hypothetical distance between New York and Boston. For simplicity, let's it's 120 miles. So during the first trip, John took 120 mi/60 mph = 2 hours to travel. On the way back, he took 120/40 = 3 hours. Average speed is just (total distance)/(total time).

Therefore, average speed = (240 miles)/(5 hours) = 48 mph.

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