Question

A train Travels the first 30 km of 120 km track with a uniform speed of 30 km/h . what should be the speed of the train to cover the remaining distance of the track so that its average speed is 60 km/hr for the entire trip.

Answer 1

For this problem, We have to use the average Speed formula.
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As it is given that,

Speed in the first Part of the journey,S(1)

= 30 km/ hr

Speed in the 2nd Part of the journey,S (2)

= ? km/hr

Average Speed(s) = 60km/hr

So by using,

Average speed (s)= [S(1) + S(2)]/2

60 = [30 + S (2)]/2

120 = 30 + S (2)

(S) = 120-30

= 90 km/hr

Answer 2

                           ANSWER                            

                          In the first 30 km speed of the train, v1 = 30 km/h

                          Speed of the train in the next 90 km, v2 (to be determined)

                         Average speed = 60 km/h = (v1 + v2)/2  

                                         = (30 km/h + v2)/2  

                              → v2 = 90 km/h