document.write( "Question 722529: An airplane takes 3 hours to travel a distance of 1680 miles with the wind. The return trip takes 4 hours against the wind. Find the speed of the plane in still air and the speed of the wind. \n" ); document.write( "

Algebra.Com's Answer #442763 by mananth(16946) $\"\"$ $\"About$

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Plane speed =x mph
\n" ); document.write( "wind speed =y mph
\n" ); document.write( "against wind 4 hours
\n" ); document.write( "with wind 3 hours
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\n" ); document.write( "Distance against 1680 miles distance with 1680 miles
\n" ); document.write( "t=d/r against wind -
\n" ); document.write( "1680 / ( x - y )= 4
\n" ); document.write( "4 ( x - y ) = 1680
\n" ); document.write( "4 x - 4 y = 1680 ....................1
\n" ); document.write( "
\n" ); document.write( "1680 / ( x + y )= 3
\n" ); document.write( "3 ( x + y ) = 1680
\n" ); document.write( "3 x + 3 y = 1680 ...............2
\n" ); document.write( "Multiply (1) by 3
\n" ); document.write( "Multiply (2) by 4
\n" ); document.write( "we get y
\n" ); document.write( "12 x + -12 y = 5040
\n" ); document.write( "12 x + 12 = 6720
\n" ); document.write( "24 x = 11760
\n" ); document.write( "/ 24
\n" ); document.write( "x = 490 mph
\n" ); document.write( "
\n" ); document.write( "plug value of x in (1) y
\n" ); document.write( "4 x -4 y = 1680
\n" ); document.write( "1960 -4 -1960 = 1680
\n" ); document.write( "-4 y = 1680
\n" ); document.write( "-4 y = -280 mph
\n" ); document.write( " y = 70
\n" ); document.write( "Plane speed 490 mph
\n" ); document.write( "wind speed 70 mph
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\n" ); document.write( "m.ananth@hotmail.ca
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