Question

A train travel from Kolkata to burdwan at a speed of 45km/hr, and return to Kolkata at a speed of 36km/hr. What is the average speed of the train over the whole journey?

Answer 1

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Answer 2

Answer:

40 km/hr.

Step-by-step explanation:

Let the distance from Kolkata to burdwan  be x

A train travel from Kolkata to burdwan at a speed of 45 km/hr

So, $Time = \frac{Distance}{Speed}$

$Time = \frac{x}{45}$

A train  return to Kolkata at a speed of 36 km/hr.

So, $Time = \frac{Distance}{Speed}$

$Time = \frac{x}{36}$

$\text{Average speed}=\frac{\text{Total Distance}}{\text{Total Time}}$

$\text{Average speed}=\frac{x+x}{\frac{x}{45}+\frac{x}{36}}$

$\text{Average speed}=\frac{2x}{\frac{x}{20}}$

$\text{Average speed}=2x\times \frac{20}{x}$

$\text{Average speed}=40$

Hence the average speed of the train over the whole journey is 40 km/hr.