SOLUTION: Jeff bicycles 120 miles at the rate of r mph. The same trip would have taken 5 hours longer if he had decreased his speed by 4 mph. Find r. I thought it would be 120/(r-4)-120r=

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Question 1158942: Jeff bicycles 120 miles at the rate of r mph. The same trip would have taken 5 hours longer if he had decreased his speed by 4 mph. Find r.
I thought it would be 120/(r-4)-120r=5. It doesn't make sense when I work it out
Found 3 solutions by Alan3354, ikleyn, MathTherapy:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Jeff bicycles 120 miles at the rate of r mph. The same trip would have taken 5 hours longer if he had decreased his speed by 4 mph. Find r.
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t = d/r = 120/r
t+5 = d/(r-4)
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Can you do the rest?

Answer by ikleyn(53765) About Me  (Show Source):
You can put this solution on YOUR website!
.

The "time" equation is


    120%2F%28r-4%29 - 120%2Fr = 5 hours longer.


Reduce it to a quadratic equation and solve it formally.


Or guess the answer mentally:  r = 12 miles per hour.    ANSWER


CHECK.  120%2F%2812-4%29%29 - 120%2F12 = 120%2F8 - 120%2F12 = 15 - 10 = 5 hours.   ! Correct !

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Solved/explained/answered.

If you still have questions, do not hesitate to post them to me.

Please refer to the problem ID number 1158942.



Answer by MathTherapy(10810) About Me  (Show Source):
You can put this solution on YOUR website!
Jeff bicycles 120 miles at the rate of r mph. The same trip would have taken 5 hours longer if he had decreased his speed by 4 mph. Find r.
I thought it would be 120/(r-4)-120r=5. It doesn't make sense when I work it out
Doesn't make sense because you should've had: