SOLUTION: if a car travelled 5 kilometer an hour faster it would take one hour les to travel 210 km.What is the speed of car and what time does it take.

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Question 518908: if a car travelled 5 kilometer an hour faster it would take one hour les to travel 210 km.What is the speed of car and what time does it take.
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
original time - time after speed increase =1
t=d/r
d=210
r=x
210/x -210/(x+5)=1
multiply by the LCD x(x+5)
210(x+5)-240x=x(x+5)
210x+1050-210x=x^2+5x
x^2+5x-1050=0
Find the roots of the equation by quadratic formula

a= 1 , b= 5 , c= -1050

b^2-4ac= 25 + 4200
b^2-4ac= 4225 %09sqrt%28%094225%09%29=%0965%09
x=%28-b%2B-sqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=%28-b%2Bsqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=( -5 + 65 )/ 2
x1= 30
x2=( -5 -65 ) / 2
x2= -35
Ignore negative value
speed = 30 mph
m.ananth@hotmail.ca