SOLUTION: A car travels at a constant speed to cover a distance of 460km. If its speed is increased by 15km/h, the time will decrease by 90 min. what is the speed of the car?

Question 982790: A car travels at a constant speed to cover a distance of 460km. If its speed is increased by 15km/h, the time will decrease by 90 min. what is the speed of the car?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!

let speed of car be x
time taken = 460/x
speed increased by 15 km/h
new speed = x+15
new time = 460/(x+15)
saves 1.5 hours =3/2
460/x - 460/(x+15) = 3/2
(460(x+15)-460x)/x(x+15) = 3/2
460x+6900-460x = (x^2+15x)*3/2
6900*2/3 =(x^2+15x)
4600 = x^2+15x
x^2+15x-4600=0
solve the quadratic equation
x= speed =60.7 km/h

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