Question

On a 120 km track a train travel the first 30 km at a uniform speed of 30km/h.how fast the train travel the next 120 km so as to average 60km/h for the entire trip

Answer 1

The ans. is 90 km/hr.

Answer 2

AVERAGE SPEED = TOTAL DISTANCE/TIME TAKEN

AVERAGE SPEED =

$60 = \frac{120}{ \frac{30}{30} + \frac{90}{x} } \\ 60 = \frac{120}{1 + \frac{90}{x} } \\ 60 = \frac{120}{ \frac{(x + 90)}{x} } \\ 60 = \frac{120x}{x + 90} \\ 60x + 5400 = 120x \\ 60x = 5400 \\ x = 90$

TRAIN SHOULD TRAVEL AT THE SPEED OF 90 KMPH SO AS TO AVERAGE SPEED WILL BE 60 KMPH ENTIRE THE TRIP.

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