If a train runs at 6/7th of its original speed, then it reaches the station 20 minutes late. Find out the usual time taken by train to cover the distance.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 120 minutes.
Let the original speed of the train be S and the original time taken be T
The train is late by 20 minutes
New time = T + 20 minutes
Distance = speed × time
⇒ S × T = (6S/7) × (T + 20/60)
⇒ T = 6/7(T + 1/3)
⇒ 7T = 6(T + 1/3)
⇒ 7T = 6T + 2
⇒ 7T - 6T = 2
⇒ T = 2 hours or 120 minutes