SOLUTION: if a cyclist had gone 3km per hour faster, he would have have taken 1 hour and 20 minutes less to ride 80kms. What time did he take

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Question 1105089: if a cyclist had gone 3km per hour faster, he would have have taken 1 hour and 20 minutes less to ride 80kms. What time did he take
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
                SPEED      TIME        DISTANCE

DONE              r         80/r          80

IF               r+3       80/(r+3)       80

DIFFERENCE                 1%261%2F3


He took 80%2Fr hours for the trip.
highlight_green%2880%2Fr-80%2F%28r%2B3%29=1%261%2F3%29
-
80%2Fr-80%2F%28r%2B3%29=4%2F3
20%2Fr-20%2F%28r%2B3%29=1%2F3
60%2Fr-60%2F%28r%2B3%29=1
60%28r%2B3%29-60r=r%5E2%2B3r
60r%2B180-60r=r%5E2%2B3r
180=r%5E2%2B3r
r%5E2%2B3r-180=0
%28r-12%29%28r%2B15%29=0
-
highlight_green%28r=12%29

Time taken was 80%2F12=40%2F6=20%2F3=highlight%286%262%2F3%29, hours.
6 hours 40 minutes