SOLUTION: a car travels at constant speed from q to r , a distance of 300 km apart . if the driver increases the speed by 5 km/hr , the journey will take 2 hours less .find the original spee

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Question 810417: a car travels at constant speed from q to r , a distance of 300 km apart . if the driver increases the speed by 5 km/hr , the journey will take 2 hours less .find the original speed of the car.
Answer by ankor@dixie-net.com(22740) (Show Source):
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a car travels at constant speed from q to r , a distance of 300 km apart .
if the driver increases the speed by 5 km/hr , the journey will take 2 hours less .
find the original speed of the car.
:
Let s = the original speed
then
(s+5) = the faster speed
:
Write a time equation, time = dist/speed
:
original time - faster time = 2 hr
- = 2
multiply by s(s+5) and you have
300(s+5) - 300s = 2s(s+5)
300s + 1500 - 300s = 2s^2 + 10s
arange as a quadratic equation on the right
0 = 2s^2 + 10s - 1500
you can use the quadratic formula but this will factor to
(2s-50)(s+30) = 0
The positive solution is all we want here
2s = 50
s = 25 km/hr is the original speed
:
:
check this by finding the actual time at each speed
300/25 = 12 hrs
300/30 = 10 hrs, a 2 hr difference