Question 187089
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Use *[tex \Large d = rt \ \ \Rightarrow\ \ t = \frac{d}{r}]


Fred's trip:


<i>d</i> = 40 km, <i>t</i> unknown, but the same as Samantha's trip, <i>r</i> = Fred's rate of speed -- the answer we seek.


Samantha's trip:


<i>d</i> = 68 km, <i>t</i> unknown, but the same as Fred's trip, <i>r</i> = Fred's rate of speed so <i>r</i> + 7 = Samantha's rate of speed.


For Fred:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \  t = \frac{40}{r} ]


For Samantha:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \  t = \frac{68}{r+7}]


But <i>t</i> = <i>t</i>, so:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \  \frac{68}{r+7} = \frac{40}{r}]


Solve for <i>r</i> to get Fred's speed.  Hint: First cross-multiply.


John
*[tex \LARGE e^{i\pi} + 1 = 0]
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