SOLUTION: A plane reaches 1200 Km 1 hr earlier, if the speed of the plane is increased by 60km/hr from its initial speed. what is the initial speed of the plane?

Algebra.Com
Question 205849: A plane reaches 1200 Km 1 hr earlier, if the speed of the plane is increased by 60km/hr from its initial speed. what is the initial speed of the plane?
Answer by AndrewRyan(3)   (Show Source): You can put this solution on YOUR website!
(x+60) [(1200/x)-1] = 1200
1200 - x + (72000/x) - 60 = 1200
x(1200 - 60 - x + (72000/x) = 1200)
1140x - x^2 + 72000 = 1200x
-x^2 + 1140x - 1200x + 72000 = 0
-x^2 - 60x + 72000 = 0
x^2 + 60x - 72000 = 0
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation (in our case ) has the following solutons:



For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=291600 is greater than zero. That means that there are two solutions: .




Quadratic expression can be factored:

Again, the answer is: 240, -300. Here's your graph:

(x - 240)(x + 300)
x = 240; x = -300 [-300 will be ignored because there is no negative speed]
x = 240
checking:
(240+60) [(1200/240)-1] = 1200
(300) (5 - 1) = 1200
(300) (4) = 1200
1200 = 1200
x = 240 is a solution
RELATED QUESTIONS

Plane flies 540 km/hour west into a wind that is 60km/hr east. What is the velocity? I... (answered by stanbon)
Help me to solve this problem: A plane takes 10 hours less to travel 1200 km than a... (answered by Alan3354,josgarithmetic,ikleyn)
A plane is heading due south and climbing at the rate of 110 km/hr. If its airspeed is... (answered by Alan3354)
a car travels from a to b in 45 mins with speed of 40 km/hr .if the speed is increased... (answered by josgarithmetic)
A train travels half the distance from 30 km/hr and the remaining half with 60km/hr. What (answered by Alan3354)
Airplane A travels 2800 km at a certain speed. Airplane B travels 2000 km at a speed 50... (answered by ptaylor)
27) A train travels 150 km in the same time that a plane covers 400 km. If the speed of... (answered by drj)
a train travels 150 km in the same time that a plane covers 400 km. if the speed of the... (answered by stanbon)
A train travels 110 km in the same time that a plane covers 385 km. If the speed of the... (answered by TimothyLamb,MathTherapy)