The distance between stations A and B is 778 kilometres. A train travels from station A to station B at a uniform speed of 84 km/h and then returns to station A at a uniform speed of 56 km/h. What is the train's average speed (in km/h) throughout the journey?
Answer & explanation
Correct answer: option 3
Average Speed = \(\frac{Total\; Distance }{Total\; Time }\)
Distance = Speed × Time
Total distance = 778 + 778 = 1556 km
Time taken while going from A to B = \(\frac{778 }{84 }\) = 9.26 hours
Time taken while returning back to A = \(\frac{778 }{56 }\) = 13.89 hours
Average speed = \(\frac{1556 }{ 9.26 + 13.89 }\)
= \(\frac{1556 }{ 23.15 }\)
= 67.2 km/h