document.write( "Question 829352: A boat can travel on a river 7 miles upstream in the same time it takes to travel 9 miles downstream. Find the speed of the current if the speed of the boat in still water is 8 miles per hour. \n" ); document.write( "

Algebra.Com's Answer #499801 by TimothyLamb(4379) $\"\"$ $\"About$

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\n" ); document.write( "x = boat speed
\n" ); document.write( "y = current speed
\n" ); document.write( "x = 8 mph
\n" ); document.write( "---
\n" ); document.write( "s = d/t
\n" ); document.write( "t = d/s
\n" ); document.write( "---
\n" ); document.write( "t = 7/(x - y)
\n" ); document.write( "t = 9/(x + y)
\n" ); document.write( "---
\n" ); document.write( "7/(x - y) = 9/(x + y)
\n" ); document.write( "7(x + y) = 9(x - y)
\n" ); document.write( "7x + 7y = 9x - 9y
\n" ); document.write( "9y + 7y = 9x - 7x
\n" ); document.write( "16y = 2x
\n" ); document.write( "y = 2x/16
\n" ); document.write( "y = (2*8)/16
\n" ); document.write( "---
\n" ); document.write( "y = current speed = 1 mph
\n" ); document.write( "---
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