SOLUTION: a person traveling 210 km by car drove the first part at 100 km/h and the rest at 80 km/h. If the trip took 2.25 h to complete, what distance was traveled at 100 km/h.

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Question 162900: a person traveling 210 km by car drove the first part at 100 km/h and the rest at 80 km/h. If the trip took 2.25 h to complete, what distance was traveled at 100 km/h.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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a person traveling 210 km by car drove the first part at 100 km/h and the rest at 80 km/h. If the trip took 2.25 h to complete, what distance was traveled at 100 km/h.
:
Let d = distance traveled at 100 km/h
:
The total distance is given as 210 km, therefore:
(210-x) = distance traveled at 80 km/h
:
Write a time equation: time = distance%2Fspeed
:
100km/hr time + 80km/hr time = 2.25 hrs
d%2F100 + %28%28210-d%29%29%2F80 = 2.25
:
Multiply equation by 400
400*d%2F100 + 400*%28%28210-d%29%29%2F80 = 400(2.25)
:
Cancel the denominator out and you have:
4d + 5(210-d) = 900
:
4d + 1050 - 5d = 900
:
4d - 5d = 900 - 1050
:
-d = -150
:
d = 150 km at 100 km/hr
then
210 - 150 = 60 km at 80 km/hr
:
:
Check solution by finding the times
150/100 = 1.5 hr
60/80 = .75 hrs
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total hr 2.25