A boat's speed while moving downstream is 60% higher than its speed while moving upstream. If the boat covers 720 km downstream in 18 hours, determine its speed in still water.

ATQ; Let the speed of the boat in still water and the speed of the stream be ‘x’ km/h and ‘y’ km/h, respectively. Downstream speed of the boat = (x + y) km/h Upstream speed of the boat = (x – y) km/h Downstream speed of the boat = (720/18) = 40 km/h
According to the given condition, (x + y) = 40 ------- (I) And, 40 = 1.6 × (x – y) Or, (x – y) = 40 / 1.6 = 25 -------- (II) By adding equation (I) and equation (II), we get x = 32.5 km/h Therefore, the speed of the boat in still water = 32.5 km/h