Question

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On a 120 km tracks a train travels the first 30 km at a uniform speed of 45 km per hour. How fast must the train travel the next 90 km so as to average 60 km per hour for the entire trip ?

Answer 1

Total Distance travelled by the train = 30+90=120 km

Average speed = 60 km h^-1

Total Time taken =120/60 = 2 h

Time taken for the first 30 km at a speed of 45 km h^-1 = 30/45 = 2/3 h.

Thus train has to cover balance 90 km in 2 - 2/3 = 4/3 h

Hence required speed will be 90×3/4 = 67.5 km h ^-1 Answer

Answer 2

Average speed = total distance / total time taken..

60 km/ h = 120km / 1 hour + 90 / v2 hours...

After this i don't know sorry