# SOLUTION: Please help me set up this problem: "When Ace Airlines changed to planes that flew 100km/hour faster than its old ones, the time of its 2800 km Dallas-Seattle flight was reduced

Algebra ->  Algebra  -> Rational-functions -> SOLUTION: Please help me set up this problem: "When Ace Airlines changed to planes that flew 100km/hour faster than its old ones, the time of its 2800 km Dallas-Seattle flight was reduced      Log On

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 Click here to see ALL problems on Rational-functions Question 427559: Please help me set up this problem: "When Ace Airlines changed to planes that flew 100km/hour faster than its old ones, the time of its 2800 km Dallas-Seattle flight was reduced by 30 minutes. Find the speed of the new planes."Answer by mananth(12270)   (Show Source): You can put this solution on YOUR website!original speed = x increased speed = x+100 ... Original time = 2800/x Time after speed increase = 2800/(x+100) 2800/x - 2800/(x+100)=1/2 LCD = x(x+100) multiply by x(x+100) 2800(x+100)-2800*x= 1/2* x(x+100) 2800x+280000-2800x=1/2(x^2+100x) 5600x+560000-5600x= x^2+100x x^2+100x-560000=0 Find the roots of the equation by quadratic formula a= 1 ,b= 100 ,c= -560000 b^2-4ac= 10000 + 2240000 b^2-4ac= 2250000 x1=( -100 + 1500 )/ 2 x1= 700 x2=( -100 -1500 ) / 2 x2= -800 Ignore negative value plane speed = 700 mph New plane speed = 800 mph