Question

A truck travelled the first one-third of the distance d at a speed of 10 kmh−1, the second one-third of the distance at a speed of 12 kmh−1 and the last one-third of the distance at a speed of 20 kmh−1. The average speed of the truck is approximately equal to (in kmh−1)10131517

Solution

The correct option is B 13Using   speed= distance travelledtime taken Time taken to travel first one-third of the distance =d310 Time taken to travel second one-third of the distance  =d312 Time taken to travel last one-third of the distance =d320 ⇒Average speed=d3+d3+d3d310+d312+d320 =dd30+d36+d60=36028=12.8 km/h≈13 km/h

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