document.write( "Question 568773: A motorboat can maintain a constant speed of 16 miles per hour relative to the water. The boat makes a trip upstream to a certain point in 20 minutes; the return trip takes 15 minutes. What is the speed of the current? \n" ); document.write( "
Algebra.Com's Answer #367126 by mananth(16946)\"\" \"About 
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speed of current be x mph\r
\n" ); document.write( "\n" ); document.write( "let the distance traveled be y\r
\n" ); document.write( "\n" ); document.write( "upstream speed = 16-x
\n" ); document.write( "downstream speed = 16+x mph\r
\n" ); document.write( "\n" ); document.write( "distance / speed = time\r
\n" ); document.write( "\n" ); document.write( "y/(16-x)= 1/3\r
\n" ); document.write( "\n" ); document.write( "3y=(16-x)\r
\n" ); document.write( "\n" ); document.write( "3y=16-x
\n" ); document.write( "3y+x=16-------------------(1)\r
\n" ); document.write( "\n" ); document.write( "y/(16+x)= 1/4
\n" ); document.write( "4y=(16+x)
\n" ); document.write( "4y=16+x
\n" ); document.write( "4y-x=16...................(2)\r
\n" ); document.write( "\n" ); document.write( "x+3y=16 .............1
\n" ); document.write( "-x+4y= 16 .............2
\n" ); document.write( "Eliminate
\n" ); document.write( "multiply (1)by -4
\n" ); document.write( "Multiply (2) by 3
\n" ); document.write( "-4x-12y =-64
\n" ); document.write( "-3x+12y =48
\n" ); document.write( "Add the two equations
\n" ); document.write( "-7x=-16
\n" ); document.write( "/ -7
\n" ); document.write( "x=2.29
\n" ); document.write( "plug value of x in (1)
\n" ); document.write( "x+3y=16
\n" ); document.write( "2.29+3y =16
\n" ); document.write( "3y = 16-2.29
\n" ); document.write( "3y = 13.71
\n" ); document.write( "y = 4.57 miles\r
\n" ); document.write( "\n" ); document.write( "speed of current = 2.29 mph
\n" ); document.write( " \r
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