Question 1122555
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<pre>
Walking at the speed of 4 km/h, the man spends 1.5 hours to cover 6 kilometers.


For the way back, moving at the speed of 12 km/h, he spends 0.5 of an hour.


In all, he spends 1.5 hours + 0.5 of an hour = 2 hours to cover 6 + 6 = 12 kilometers.


It means that his average speed on the way "to there" and back is  {{{12/2}}} = 6 kilometers per hour.
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Solved.


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<U>The lesson to learn from the solution is THIS</U> :


<pre>
    Notice that the average speed in this case  "6 km/h" IS NOT the average of the partial speeds  4 km/h  and  12 km/h/
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