Given: Boat covers 50 km distance in still water = 5 hrs Speed of current = 5 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: Speed of boat in still water = 50/5 = 10 km/hr Upstream speed = 10 – 5 = 5 km/hr ∴ Time taken by boat to cover 50 km upstream = 50/5=10 hrs