Question
A motor boat covers a certain distance downstream in a
river in 3 hours. It covers the same distance upstream in 3 hours and 30 minutes. If the speed of water is 1.25 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 + 1.25) km/hr Rate upstream = (x – 1.25) km/hr According to the question, y/(x + 1.25) = 3 --- (i) y/(x – 1.25) = 7/2 --- (ii) On dividing equation (i) by (ii), (x – 1.25)/(x + 1.25) = 3/(7/2) = 6/7 7x – 8.75 = 6x + 7.5 x = 8.75 + 7.5 = 16.25 kmph
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