With an average speed of 42 km/h, a train reaches its destination in time. If it moves with an average speed of 14 km/h, it is late by 35 minutes. The length of the journey is:

12.25 km

As per the question,

The ratio of

average speed    42 : 14

                           3 : 1

Time                    1 : 3

( Time is inversely proportional ti Speed )

Difference 2R = 35 minutes

2R = \(\frac{35}{60}\)

1R = \(\frac{7}{24}\)

Now the distance,

 Distance  = 42 × \(\frac{7}{24}\)  = 12.25 km