<PRE><B>Question 565942</B>
Plane   	speed	x   	mph	
wind   	speed	40	mph	
				
against   	wind   	x-	40	mph
with   	wind   	x+	40	mph
				
Distance= 	600	miles		
				
Time against + time with  = 8	hours
t=d/r		

600/(x+40)+600/(x-40)=	8
													
LCD =	(x-40)(x+40)				
600	*(x-40)+600(x+40)=8
600x-24000+600x+24000=8(x ^2-1600)
1200x=	8x ^2-12800							
8x ^2-1200x-12800

8x^2+80x-1280x-12800=0
8x(x+10)-1280(x+10)=0

(x+10)(8x-1280)=0
8(x+10)(x-160)=0
x=160 which is positive

speed of plane = 160 mph							
		
</PRE>