A car travels at a soeed of 40 km/h dor 10 mins. , then at 55 km/h for 20 mins and finally at 20 km/ h for 20 mins. What is the average speed of the car?

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Solution

Let the distance travelled in three intervals be x, y and z.
So, x = 40Ã—(10/60) = 6.67 km
y = 55Ã—(20/60) = 18.33 km
z = 20Ã—(20/60) = 6.67 km
Total distance = x +y + z = 31.67 km
Average speed = Total distance / Total time = 31.67/(5/6) = 38 km/h

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