SOLUTION: When Ace Airlines changed to planes that flew 100 km/h faster than its old ones, the time of its 2800 km Dallas-Seattle flight was reduced by 30 min. Find the speed of the new pla

Algebra ->  Percentage-and-ratio-word-problems -> SOLUTION: When Ace Airlines changed to planes that flew 100 km/h faster than its old ones, the time of its 2800 km Dallas-Seattle flight was reduced by 30 min. Find the speed of the new pla      Log On


   

Question 72139This question is from textbook Algebra and Trigonometry: Structure and Method
: When Ace Airlines changed to planes that flew 100 km/h faster than its old ones, the time of its 2800 km Dallas-Seattle flight was reduced by 30 min. Find the speed of the new plane. This question is from textbook Algebra and Trigonometry: Structure and Method

Answer by checkley75(3666) About Me  (Show Source):
You can put this solution on YOUR website!
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