Correct Answer - Option 1 : 45 km/h
Let the speed of the train be x km/hr and the length of the train be d m.
As we know
Distance = Speed × Time
⇒ Distance = x × 5/18 × 20 ----(i)
Again,
Distance = 18 × (x + 5) × 5/18 ----(ii)
From equation (i) and equation (ii), we get
⇒ x × 5/18 × 20 = 18 × (x + 5) × 5/18
⇒ 20x = 18x + 90
⇒ 20x - 18x = 90
⇒ 2x = 90
⇒ x = 90/2
∴ x = 45 km/hr