The distance between Delhi and Gwalior is 350 km. A bus travels the first 175 km at a speed of 60 km/h. How fast should be the bus travel the next distance of 175km so as to cover the average speed of 80 km/h for the whole journey?
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Answers
Answer:
this is the right answer
Answer:
As soon as you read the word average, it becomes tempting to simply add up the speeds and halve them to get the answer. But this logic is flawed.
Let’s get back to the definition of average speed.
Average speed is the total distance travelled by an object divided by the total time taken to cover that distance.
Let us say the distance between delhi and agra is ‘d’ kms. So for a return trip, our guy covers a total distance of ‘2d’ kms.
From Delhi to Agra:
Speed = 30km/h
Time = d/30 hrs (because time = distance/speed)
From Agra to Delhi:
Speed = 60km/h
Time = d/60 hrs
To sum up:
Total distance travelled = 2d kms
Total time taken = d/30 + d/60 hrs
Avg speed = Total distance / Total time
On calculation,
Avg speed = 40 km/h