document.write( "Question 615280: A plane flew 720 miles in 3 hours with the wind. It would take 4 hours to travel the same distance against the wind. What is the rate of the plane in still air? What is the speed of the wind? \n" ); document.write( "

Algebra.Com's Answer #387083 by mananth(16946) $\"\"$ $\"About$

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Plane speed =x mph
\n" ); document.write( "wind speed =y mph
\n" ); document.write( "against wind x-y 4 hours
\n" ); document.write( "with wind x+y 3 hours
\n" ); document.write( "
\n" ); document.write( "Distance against wind 720 miles distance with wind 720 miles
\n" ); document.write( "t=d/r against wind
\n" ); document.write( "720 / ( x - y )= 4
\n" ); document.write( "4 ( x - y ) = 720
\n" ); document.write( "4 x - 4 y = 720 ....................1
\n" ); document.write( "with wind
\n" ); document.write( "720 / ( x + y )= 3
\n" ); document.write( "3 ( x + y ) = 720
\n" ); document.write( "3 x + 3 y = 720 ...............2
\n" ); document.write( "Multiply (1) by 3
\n" ); document.write( "Multiply (2) by 4
\n" ); document.write( "we get
\n" ); document.write( "12 x + -12 y = 2160
\n" ); document.write( "12 x + 12 y = 2880
\n" ); document.write( "24 x = 5040
\n" ); document.write( "/ 24
\n" ); document.write( "x = 210 mph
\n" ); document.write( "
\n" ); document.write( "plug value of x in (1)
\n" ); document.write( "4 x -4 y = 720
\n" ); document.write( "840 -4 y = 720
\n" ); document.write( "-4 y = 720 -840
\n" ); document.write( "-4 y = -120
\n" ); document.write( " y = 30 mph
\n" ); document.write( " plane speed 210 mph
\n" ); document.write( " wind speed= 30 mph
\n" ); document.write( " \n" ); document.write( "

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