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 3.5 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 + 3.5) km/hr Rate upstream = (x – 3.5) km/hr According to the question, y/(x + 3.5) = 2 --- (i) y/(x – 3.5) = 5/2 --- (ii) On dividing equation (i) by (ii), (x – 3.5)/(x + 3.5) = 2/(5/2) = 4/5 5x – 16.5 = 4x + 15 x = 16.5 + 15 = 31.5 kmph
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