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=

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)   (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)   (Show Source): You can put this solution on YOUR website!
.

The "time" equation is - = 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. - = - = 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)   (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:
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