<PRE><B>Question 72139</B>
2800/(X+100)+.5=2800/X
(2800+.5X+50)/(X+100)=2800/X 
(2850+.5X)/(X+100)=2800/X NOW CROSS MULTIPLY
(X+100)2800=X(2850+.5X)
2800X+280000=2850X+.5X^2
.5X^2+50X-280000=0
X^2+100X-560000=0
(X-700)(X+800)=0
X-700=0
X=700 ANSWER FOR THE SPEED OF THE SLOWER AIRPLANE
X+100=800 IS THE SPEED OF THE FASTER PLANE.
PROOF
2800/800+.5=2800/700
3.5+.5=4
4=4
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