document.write( "Question 719418: A pilot can fly a plane at 75 mph in calm air. A recent trip of 300 mi flying with the wind and 300 mi returning against the wind took 9 h. Find the rate of the wind. \n" ); document.write( "
Algebra.Com's Answer #441347 by graphmatics(170)\"\" \"About 
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Let x be the speed of the wind. Then 75+x is the speed of the plane flying with the wind and 300/(75+x) is the amount of time the plane flew with the wind. Similarity 75-x is the speed of the plane flying against the wind and 300/;(75-x) is the amount of time the plane flew against the wind. As we are given that the amount of time the plane flew with and against the wind is 9 hours we have that
\n" ); document.write( "300/(75+x)+300/(75-x)=9
\n" ); document.write( "(75+x)*(75-x)*300/(75+x) + (75+x)*(75-x)*300/(75-x)=(75+x)*(75-x)*9
\n" ); document.write( "(75-x)*300 + (75+x)*300=(75+x)*(75-x)*9
\n" ); document.write( "22500-300*x + 22500+300*x=(5625-x^2)*9
\n" ); document.write( "45000=50625-9*x^2
\n" ); document.write( "9*x^2-5625=0
\n" ); document.write( "(3*x)^2-75^2=0
\n" ); document.write( "(3*x-75)*(3*x+75)=0
\n" ); document.write( "3*x-75=0, 3*x+75=0
\n" ); document.write( "x=25, x=-25
\n" ); document.write( "As the speed of the wind must be positive we know it is 25.
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