SOLUTION: A car travels 840 mi. A second car, traveling 2 mph faster than the first car, makes the same trip in 1 h less time. Find the speed of each car.

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Question 887893: A car travels 840 mi. A second car, traveling 2 mph faster than the first car, makes the same trip in 1 h less time. Find the speed of each car.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A car travels 840 mi.
A second car, traveling 2 mph faster than the first car, makes the same trip in 1 h less time.
Find the speed of each car.
:
Let s = the 1st car speed
then
(s+2) = the 2nd car speed
:
Write a time equation; time = dist/speed
1st car time - 2nd car time = 1 hr
840%2Fs - 840%2F%28%28s%2B2%29%29 = 1
multiply by 2(s+2), cancel the denominators and you have
840(s+2) - 840s = s(s+2)*1
840s + 1680 - 840s = s^2 + 2s
Form a quadratic equation
s^2 + 2s - 1680 = 0
Factors to
(s+42)(s-40) = 0
The positive solution is what we want here
s = 40 mph is the speed of the 1st car
:
I'll let you find the speed of the 2nd car, check your solutions in the original time equation