A car travelled the first one-third of the distance d at a speed of 20kmh−1, the second one-third of the distance at a speed of 40kmh−1 and the last one-third of the distance at a speed of 120kmh−1. Determine the average speed of the car.
A
18km/h
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B
27km/h
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C
36km/h
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D
45km/h
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Solution
The correct option is C36km/h We know that speed=distance travelledtime taken
Time taken by the car to travel first one-third of the distance =d320
Time taken by the car to travel second one-third of the distance =d340
Time taken by the car to travel last one-third of the distance =d3120
Average speed=Total distance travelledTotal time taken