Question 681775
Plane  	speed	=x	mph					
wind   	speed	=y	mph					
Against windx-y		2.5	hours					
with wind x+y		2	hours					
								
Distance = 		1380	miles		distance=		1380	
t=d/r	against	wind   						
1380.00	/	(	x	-	y	)=	2.50	
								
2.50	x	-	-2.50	y	=	1380.00	....................1	
with wind x+y								
1380.00	/	(	x	+	y	)=	2.00	
2.00	(	x	+	y	)	=	1380.00	
2.00	x	+	2.00	y	=	1380.00	...............2

Eliminate y in the linear system	
Multiply (1) by	2.00							
Multiply (2) by	2.50							
we get				y				
5.00	x	+	-5.00	y	=	2760.00		
5.00	x	+	5.00		=	3450.00		
10.00	x	=	6210.00					
/	10.00							
x	=	621	mph					
								
plug value of x in (1)				y				
2.5	x		-2.5	y	=	1380		
1552.5			-2.5	-1552.5	=	1380		
-2.5	y	=	1380					
-2.5	y	=	-172.5	mph				
	y	=	69					
	Plane  	621	mph					
	wind   	69	mph	


				
								
CHECK								
x+y=	690							
X-y=	552			+				
1380.00	/	(	690.00			)=	2	
1380	/	(	552	)		=	2.5