Correct Answer - Option 1 : 39 km/h
Given:
Total distance to be covered = 624 km
Formula used:
Time = Distance/Speed
Calculation:
Let the speed of train B and train A be y km/hr and x km/hr respectively
Accroding to the question
624/x = 624/y + 6
Let, 624/x = A and 624/y = B
⇒ A = B + 6 ----(1)
Now, if the speed of train A is doubled, it takes 5 hours less than the train B
⇒ 624/2x = (624/y) - 5
⇒ A/2 = B - 5
⇒ A = 2B - 10 ----(2)
From equation (1) and (2), we get
⇒ B + 6 = 2B - 10
⇒ B = 16
⇒ 624/y = 16
⇒ y = 624/16 = 39
∴ The speed of the train B is 39 km/hr