Given: Ratio of the speeds of two train = 3 : 4 Second train covers 300 km in = 3 hr Formula: Speed = Distance/Time Calculation: Speed ratio of two trains = 3x : 4x Speed of second train = 300/3 = 100 km/hr ⇒ 4x = 100 ⇒ x = 100/4 ⇒ x = 25 km/hr ∴ Speed of first train = 3 × 25 = 75 km/hr 4 unit = 300/3 = 100 km/hr ∴ 3 unit = (100/4) × 3 = 75 km/hr