Tips & Tricks Given: Motor boat goes 48 km downstream = 4 hrs Motor boat goes 20 km upstream = 10 hrs Formula: Speed = Distance/Time If speed of motor 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 motor boat and current be x km / hr and y km / hr respectively, According to the question (x + y) = 48/4 ⇒ (x + y) = 12 ---(1) (x – y) = 20/10 ⇒ (x – y) = 2 ---(2) Adding equation (1) and equation (2), we get 2x = 14 ⇒ x = 7 ∴ Speed of motor boat in still water is 7 km/hr.