Question 1149792
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<pre>
If x is the slower rate (in miles per hour), then the faster rate is (x+9) mph.


The "time" equation is


    {{{60/x}}} + {{{60/(x+9)}}} = 3  hours.


Simplify


    {{{20/x}}} + {{{20/(x+9)}}} = 1


then multiply both sides by x*(x+9)


    20*(x+9) + 20x = x*(x+9)

    20x + 180 + 20x = x^2 + 9x

    x^2 - 31x - 180 = 0

    {{{x[1,2]}}} = {{{(31 +- sqrt(31^2 + 4*180))/2}}} = {{{(31 +- sqrt(1681))/2}}} = {{{31 +- 41)/2}}}.


Only positive root makes sense  x = {{{(31+41)/2}}} = 36.


<U>Answer</U>.  The slower rate is 36 mph;  the faster rate is  36+9 = 45 mph.
</pre>

Solved.


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Using &nbsp;"time" &nbsp;equation is the &nbsp;STANDARD &nbsp;method of solving such problems.

From this lesson, &nbsp;learn on how to write, &nbsp;how to use and how to solve a &nbsp;"time" &nbsp;equation.


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