Speed of a boat in still water is three times the speed of the boat in upstream. If the boat takes 40 minutes to cover 15 km in downstream, then find the speed of the boat in still water.
Let speed of the boat in still water be ‘3x’ km/h. Speed of the boat in upstream = 3x ÷ 3 = ‘x’ km/h Speed of the stream = 3x – x = ‘2x’ km/h Speed of the boat in downstream = 3x + 2x = ‘5x’ km/h ATQ; (15/40) × 60 = 22.5 So, 5x = 22.5 Or, x = 4.5 So, speed of the boat in still water = 3 × 4.5 = 13.5 km/h
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