Given: Boat goes 50 km along the distance in = 10 hrs Speed of current = 2 km/hr Formula: Speed = distance/time If speed of boat and stream be x and y km/hr respectively, then Upstream speed = (x - y) km/hr Downstream speed = (x + y) km/hr Calculation: Let speed of boat be x km/hr Downstream speed = (x + 2) km/hr According to the question (x + 2) = 50/10 ⇒ (x + 2) = 5 ⇒ x = 5 – 2 ⇒ x = 3 Speed of boat is 3 km/hr Upstream speed = 3 – 2 = 1 km/hr ∴ Time taken by boat to cover 30 km upstream = 30/1 = 30 hrs