SOLUTION: A man drives 80km/h to Selfoss and 60km/h from Selfoss. What is the average speed? The answer is not 70km/h

Question 1092797: A man drives 80km/h to Selfoss and 60km/h from Selfoss. What is the average speed? The answer is not 70km/h
Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235)   (Show Source): You can put this solution on YOUR website!
distance= speed* time
Suppose Selfoss is 80 km away
it takes 1 hour to get there and 4/3 of an hour to return.
That would be 7/3 of an hour to drive 160 km
that is 160*3/7 km/h or 68.57 km/h.
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Suppose Selfoss is 60 km away.
It takes 3/4 hour to get there and 1 hour to get back or 7/4 hour to go 120 km
that is 120*4/7 or again 68.57 km/h average speed.
Answer by ikleyn(52777)   (Show Source): You can put this solution on YOUR website!
.
At given condition there is no a unique answer.

From the other side (or in contrast), it can be solved and has a unique answer under the assumption that
the distance "to there" is equal to the distance back, but it is not stated explicitly in the condition.

Lesson to learn from my explanation:

                Learn how to formulate Math problems correctly !

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Also see the lessons
    - Calculating an average speed: a train going from A to B and back
    - One more problem on calculating an average speed
in this site.

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