Question 1139969
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Let r be the original speed under the question.


Then you have this "time" equation


    {{{240/r}}} - {{{240/(r+10)}}} = {{{1/3}}}  hours.           <<<---=== Every fraction on the left side is the time to cover the distance . . . 


To solve it, multiply both sides by 3*r*(r+10). You will get


    720*(r+10) - 720r = r*(r+10)


    7200 = r^2 + 10r

    r^2 + 10r - 7200

    (r-80)*(r+90) = 0


The two root of the equation are r = 80  and  r = -90,  but only positive r = 80 km/h makes sense.


<U>ANSWER</U>. The original speed was  80 kilometers per hour.


<U>CHECK</U>.   {{{240/80}}} = 3 hours;   {{{240/90}}} = {{{2}}}{{{2/3}}} hours = 2 hours and 40 minutes;   the difference is  20 minutes.   ! Correct !
</pre>

Solved


Using "time" equation is the STANDARD way to solve such problems.


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


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