A train is walking at 6/7 of its usual speed, the train is 20 minutes too late. Find its usual time to cover the journey.  Choose the correct choice from the following:
A) 1 hour  B) 30 min  C) 3 hours 20 min  D) 2 hours 30 min  E) 2 hours

Rationale: new speed = 6 / 7 of the usual speed new time taken = 7 / 6 of the usual time taken so , ( 7 / 6 of the usual time ) - ( usual time ) = 20 min 1 / 6 of the usual time = 20 min usual time = 20 * 6 = 120 min = 2 hours correct option is e
Answer: E