SOLUTION: A car travels a distance of 9000 KM with a certain average speed. If after travelling half the distance the average speed of the car be increased by 15 Km/Hrs., the time required t

Algebra ->  Linear-equations -> SOLUTION: A car travels a distance of 9000 KM with a certain average speed. If after travelling half the distance the average speed of the car be increased by 15 Km/Hrs., the time required t      Log On


   

Question 720636: A car travels a distance of 9000 KM with a certain average speed. If after travelling half the distance the average speed of the car be increased by 15 Km/Hrs., the time required to travel 900 Km, is reduces by 11/2 hour, find the original average speed of the car.
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!

Time = distance /speed
original speed = x
450%2Fx+%2B450%2F%28x%2B15%29=+%28900%2Fx%29-+3%2F2

450%2F%28x%2B15%29-450%2Fx+=-3%2F2

450x-450(x+15) = (-3/2) ( x*(x+15)

-6750=(-3/2)(x^2+15x)
-13000=-3x^2-45x
3x^2+45x-13500=0
/3
x^2+15x-4500=0
x^2+75x-60-4500-0
(x+75)(x-60)=0
x= 60 km/h the original speed