Question

Two trains are travelling at an average speed 50 kmph and 100 kmph respectively on parallel tracks in the same direction. The fast train starts 2 hours later than the slow train. After how many kilometers does the fast train catch up with the slow train?

• A. 200

Answer 1

The correct option is A 200
Given,
Speed of fast train = 100 kmph.
Speed of slow train = 50 kmph.

Let 't' be the time taken by a the fast train to catch up with the slow train.
As the fast train starts after 2 hours later than the slow train, the slow train is in motion for 't +2' hours.

Distance travelled by the fast train = Distance travelled by the slow train

$100\text{km/hr}\times \text{t hr}=50\text{km/h}\times \text{(t + 2) h}\text{2t}=\text{t + 2}\text{t}=\text{2 hours}$
Distance travelled by fast train $=100\text{km/h}\times 2\text{h}=200$ km.

After 200 km the fast train catches up with the slow train.