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My trip to work is 120 miles. If I go 8 mph faster than my usual speed, I'll get to work 30 minutes earlier. How long does my trip take, in hours, if I go my usual speed?

 

 

Hi, what I have so far are the equations 120=rt and 

t-30 = \(\frac{120}{r+8}\)

which equals to \(t=\frac{120}{r+8}+30\)

 

However, when I plug the expression for the value of t into 120=rt I've gotten answers that don't work. Could someone explain or point out what is wrong? Thanks!

 Dec 22, 2019
edited by Guest  Dec 22, 2019
 #2
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You are mixing dimensions...

your rate is in mile per HOUR

your increase in time is in MINUTES.....convert 30 MINUTES to  1/2 hour and resolve for r

 

120/(r+8) + 1/2 = 120/r

 Dec 22, 2019
 #3
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Thanks so much!

Guest Dec 22, 2019

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