Question
What is the speed of a boat in still water?
Statement I: The boat covers 18 km in 3 hours downstream. Statement II: The boat covers the same distance in 6 hours upstream. Statement III: The speed of the stream is one –third that of boat in still water.Solution
Let the speed of the boat be u and that of the stream be v. Then, speed of boat downstream = u + v And speed of boat upstream = u – v From I u + v = 18/3 = 6 km/hr ……….. (i) From II, u – v = 18/6 = 3 km/hr ……… (ii) From statement III, v = u/3 ……….(iii) From I and II, we get u = 9/2 = 4.5 km/hr. From I and III, we get u + u/3 = 6 Or 4u = 18 u = 4.5 km/hr. Hence statement I and either II or III is sufficient to answer the question.
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