Up the Stream – Down the Stream

             While upstream, a crew can row a boat in eight and four- sevenths minutes. But if there was no stream they could row it in seven minutes less than it takes them to drift down the stream.

             Can you say how long it would take them to row down with the stream? 

Answer:  The crew can row ⅕ of the distance per minute on still water and the stream does half that distance per minute

              The difference and sum of these two fractions are ⁷ ⁄₆₀ and ¹⁷⁄₆₀. Hence, rowing against the stream would take ⁶⁰⁄₁₇ minutes and with the stream ⁶⁰⁄ ₁₇ minutes.

 The correct answer is 3 ⁹⁄₁₇ minutes.