SOLUTION: During the first part of a trip a man travels 140km at a certain speed. He travels 63km on the second part at a speed 7km slower. The total time of the trip is 3 hours. How fast di

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Question 1074383: During the first part of a trip a man travels 140km at a certain speed. He travels 63km on the second part at a speed 7km slower. The total time of the trip is 3 hours. How fast did he travel the first part of the trip?
Found 2 solutions by ikleyn, addingup:
Answer by ikleyn(52835) About Me  (Show Source):
You can put this solution on YOUR website!
.
Let "r" be the speed at the first part of the trip, in km/h.
Then the speed at the second part is (r-7) km/h.


The "time" equation is 

140%2Fr+%2B+63%2F%28r-7%29 = 3.


Solve it for "r". For it, multiply both sides of the equation by r*(r-7). You will get

140*(r-7) + 63r = 3r*(r-7).


Simplify and solve this quadratic equation.


Answer by addingup(3677) About Me  (Show Source):
You can put this solution on YOUR website!
(140/x)+(63/(x-7)) = 3
The common denominator is x(x-7). Join both equations into one:
7(29x-140)/(x(x-7)) = 3
7(29x-140) = 3x(x-7)
203x-980 = 3x(x-7)
203x-980 = 3x^2-21x
-3x^2-21x+203x-980 = 0
-(x-70)(3x-14) = 0
(x-70)(3x-14) = 0
x-70 = 0 or 3x-14 = 0
x = 70 or x = 14/3
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Let's try the 70 first:
140/70 = 2
63/(70-7) = 1
2+1 = 3 hours This is the correct answer.
:
John