SOLUTION: If a car had increased its average speed for a 210 mile journey by 5 MPH the journey would have been completed in one hour less. What was the original speed of the car for the jou

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Question 621132: If a car had increased its average speed for a 210 mile journey by 5 MPH the journey would have been completed in one hour less. What was the original speed of the car for the journey?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
If a car had increased its average speed for a 210 mile journey by 5 MPH the journey would have been completed in one hour less.
What was the original speed of the car for the journey?
:
Let s = original speed
then
(s+5) = the faster speed
:
Write a time equation; time = dist/speed
:
original time - faster time = 1 hr
210%2Fs - 210%2F%28%28s%2B5%29%29 = 1
multiply equation by s(s+5); results:
210(s+5) - 210s = 1s(s+5)
:
210s + 1050 - 210s = s^2 + 5s
Arrange as a quadratic equation
s^2 + 5s - 1050 = 0
You can use the quadratic equation, but this will factor
(s-30)(s+35) = 0
the positive solution is all we want here
s = 30 mph is the original speed
:
:
Check this out; find the actual time for each speed
210/30 = 7 hr
210/35 = 6 hrs
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differ: 1 hr