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 2.5 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 + 2.5) km/hr Rate upstream = (x – 2.5) km/hr According to the question, y/(x + 2.5) = 3 --- (i) y/(x – 2.5) = 7/2 --- (ii) On dividing equation (i) by (ii), (x – 2.5)/(x + 2.5) = 3/(7/2) = 6/7 7x – 17.5 = 6x + 15 x = 17.5 + 15 = 32.5 kmph
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