Question
A man rows a boat a certain distance downstream in 9
hours, while it takes 18 hours to row the same distance upstream. How many hours will it take him to row three-fifths of the same distance in still water?Solution
Let the speed of boat in still water =B and speed of stream =S then Distance =D ATQ- 
Both directions distance is equal = 9(B+S) =18(B-S) 9B+9S=18B-18S 27S=9B S: B=1:3 =>B=3S So now- Take time Three-fifths of the same distance in still water=(D/B)×3/5 =9(B+S) ×3/5 /B =[9(3S+S) ×3/5]/3S =36/5=7.2hours.
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