A train left New Delhi for Chennai at 10 AM | with a speed of 70 km/hr | Another Train also left New Delhi for Chennai | at 11 AM with a speed of 90 km / hr | At what time 2nd Train will overtake the first train |

The question is again rewritten here:

Question : A train left  New Delhi for Chennai at 10 AM  with a speed of 70 km/hr . Another Train also left New Delhi for Chennai  at 11 AM with a speed of 90 km / hr   .  At what time 2nd Train will overtake the first train .

Solution: The main point of understanding this sum is that the distance where the 2nd train will overtake the first one will be same . Also the time taken by the first trains will be 1 hr more than the 2nd trains.

Also remember that the slower train will take more time than the faster train.

Therefor we can create in one line .
90t = 70 (t+1) <br />
where t = time taken by the 2nd trains .
* See solution in the image also.
the distances are equal .
90t-70t=20t
:. t=70/20
:. t=3.5 Hrs
Therefor 2nd trains will overtake first one at (11 + 3.5) Hrs .
I. e. At 14:30 hrs or 2:30 pm .