SOLUTION: Can someone help me break this down? I have been working on it for an hour and I keep getting the wrong answer. Thank you. During the first part of a​ trip, a canoeist c

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: Can someone help me break this down? I have been working on it for an hour and I keep getting the wrong answer. Thank you. During the first part of a​ trip, a canoeist c      Log On


   

Question 1127952: Can someone help me break this down? I have been working on it for an hour and I keep getting the wrong answer. Thank you.
During the first part of a​ trip, a canoeist covered 70 km at a certain speed. He then traveled 30 km at a speed that was 4 ​km/h slower. If the total time for the trip was 8 ​hr, what was the speed on each part of the​ trip?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
                  speeds        times         distances

first part         r            70/r           70

second part       r-4           30/(r-4)       30

total                           8

70%2Fr%2B30%2F%28r-4%29=8

35%2Fr%2B15%2F%28r-4%29=4
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simplifies into 2r%5E2-33r%2B70=0

discriminant, 33%5E2-4%2A2%2A70=529=23%5E2;

r=%2833%2B23%29%2F4 because you will find the MINUS form will not work;

highlight%28r=13%263%2F4%29-------for the first part of trip.