document.write( "Question 903384: A crew rows 4 miles downstream and 2 miles upstream in one hour. Then it rows 6 miles downstream and 5 miles upstream in 2 hours. Find the rate of the stream and that of the crew in still water \n" ); document.write( "
Algebra.Com's Answer #547959 by mananth(16946)\"\" \"About 
You can put this solution on YOUR website!
Let speed with current = x
\n" ); document.write( "speed against current be y
\n" ); document.write( "t=d/r\r
\n" ); document.write( "\n" ); document.write( "time downstream + time upstream = total time\r
\n" ); document.write( "\n" ); document.write( "4/x +2/y = 1\r
\n" ); document.write( "\n" ); document.write( "let 1/x =a and 1/y be y
\n" ); document.write( "4a+2b=1.........................(1)\r
\n" ); document.write( "\n" ); document.write( "6/x +5/y =2
\n" ); document.write( "6a+5b=2.........................(2)\r
\n" ); document.write( "\n" ); document.write( "4 a + 2 b = 1 .............1
\n" ); document.write( "
\n" ); document.write( "6 a + 5 b = 2 .............2
\n" ); document.write( "Eliminate y
\n" ); document.write( "multiply (1)by -5
\n" ); document.write( "Multiply (2) by 2
\n" ); document.write( "-20 a -10 b = -5
\n" ); document.write( "12 a + 10 b = 4
\n" ); document.write( "Add the two equations
\n" ); document.write( "-8 a = -1
\n" ); document.write( "/ -8
\n" ); document.write( "a = 0.125 \r
\n" ); document.write( "\n" ); document.write( "x=1/a=1/0.125= 8
\n" ); document.write( "speed of boat = 8 mph
\n" ); document.write( "plug value of a in (1)
\n" ); document.write( "4 a + 2 b = 1
\n" ); document.write( "1 + 2 b = 1
\n" ); document.write( " 2 b = 1 -1
\n" ); document.write( " 2 b = 1
\n" ); document.write( " b = 0.25 \r
\n" ); document.write( "\n" ); document.write( "b=0.25 y=1/b =1/0.25= 4\r
\n" ); document.write( "\n" ); document.write( "speed of current = 4 mph
\n" ); document.write( " \n" ); document.write( "
\n" );