The speed of train in going from Bhopal to Varanasi is 100 kmph while when coming back from Varanasi to Bhopal, its speed is 80 kmph. What is the average speed during the whole journey? (correct to two decimal places)
Speed of train from Bhopal to Varanasi = 100 kmph
Speed of train from Varanasi to Bhopal = 80 kmph
Average speed = $$\dfrac{2ab}{a+b}$$ while a and b are speeds.
Therefore, Average speed = $$\dfrac{2\times100\times80}{100+80} = \dfrac{2\times100\times80}{180}$$
$$= \dfrac{800}{9} = 88.89$$ kmph
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