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express mensa puzzle 02/01/10

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alison6399 | 17:14 Sat 02nd Jan 2010 | Quizzes & Puzzles
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Hi

Please help with the following puzzle and explain your answer....my head is throbbing!!! Thanks

A fox completes the same round trip every evening. If he covers his outward journey at 175 metres per hour and he returns, over exactly the same distance, at 70 metres per hour.

What is his average speed over the entire journey?
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122.5 metres per hour
Rather than use algebra assume the journey is a 700 metres round trip
Outward journey 350m : 350m @ 175m/hour takes 2 hours
Return journey 350m: 350M @ 70m/hour takes 5 hours
So 700m completed in 7 hours = 100m/hour

The reason it is not simplify the average of 175 & 70 is the fact that the two parts of the trips take differing amounts of time.

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express mensa puzzle 02/01/10

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