A car travels from Kanpur to Delhi at an average speed of 60 km/h and returns at an average speed of 90 km/h. Find the average speed of the car in the whole journey.
- AOption (a)
65 km/h
- BOption (b)
78 km/h
- COption (c)
60 km/h
- DOption (d)
72 km/h
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Correct answer
72 km/h
Why this answer is correct
Given:
Speed from Kanpur to Delhi = 60 km/h.
Speed from Delhi to Kanpur = 90 km/h.
Formula Used:
Average speed = Total distance travelled / Total Time
Calculation:
Let the distance between Kanpur and Delhi be d km.
Time taken from Kanpur to Delhi = d / 60
Time taken from Delhi to Kanpur = d / 90
Total Distance = d + d = 2d
Total Time = (d / 60) + (d / 90)
Total Time = d(1/60 + 1/90)
Total Time = \(d(\frac{1}{60} + \frac{1}{90})\)
Total Time = \(d(\frac{3 + 2}{180})\)
Total Time = \(\frac{5d}{180}\)
Average Speed = (2d) / (\(\frac{5d}{180}\))
Average Speed = (2d × 180) / 5d
Average Speed = 360 / 5 = 72 km/h
The average speed for the whole journey is 72 km/h.




















