Question
A motor boat covers a certain distance downstream in a
river in 2 hours. It covers the same distance upstream in 2 hours and 30 minutes. If the speed of water is 3 km/h, then the speed of the boat in still water is:Solution
Let the speed of boat in still water be x km/hr and the distance be y km. Rate downstream = (x + 3) km/hr Rate upstream = (x – 3) km/hr According to the question, y/(x + 3) = 2 --- (i) y/(x – 3) = 5/2 --- (ii) On dividing equation (i) by (ii), (x – 3)/(x + 3) = 2/(5/2) = 4/5 5x – 15 = 4x + 12 x = 15 + 12 = 27 kmph
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