Question 1183698
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Certainly the textbook answer you show is not right. 24km in 40 minutes means an average speed of (24/(2/3))=36km/h.  That's not possible if the speeds for the two halves of the trip were 100km/h and 60km/h.<br>
Here is an approach to the problem very different from the one shown by the other tutor.<br>
The two distances are the same; the ratio of the two speeds is 100:60=5:3.<br>
That means the times spent at the two speeds are in the ratio 3:5.<br>
So 3/8 of the 40 minutes was spent at 100km/h and 5/8 of the 40 minutes at 60km/h.  The total distance was then<br>
{{{100((3/8)(40/60))+60((5/8)(40/60)) = 25+25 = 50}}}<br>
ANSWER: 50km<br>