Question 237085
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Let *[tex \Large r] represent the speed of the boat in still water.


Downstream trip:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 540\ =\ (r\ +\ 4)t\ \ \Rightarrow\ \ \frac{540}{r+4}\ =\ t]


Upstream trip:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 450\ =\ (r\ -\ 4)t\ \ \Rightarrow\ \ \frac{450}{r-4}\ =\ t]


So


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{540}{r+4}\ =\ \frac{450}{r-4}]


Cross-multiply:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 540r\ -\ 4(540)\ =\ 450r\ +\ 4(450)]


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 90r\ =\ 4(990)]


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ r\ =\ 4(11)\ =\ 44]



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