document.write( "Question 1139969: Mary makes monthly visits to her parents in Malacca, a distance of 240 km from Singapore.She finds that if she increases the speed by 10 km/hr , she could save a total of 20 minutes.
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Algebra.Com's Answer #760465 by ikleyn(52776) $\"\"$ $\"About$

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document.write( "Let r be the original speed under the question.\r\n" );
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document.write( "Then you have this \"time\" equation\r\n" );
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document.write( "     -  =   hours.           <<<---=== Every fraction on the left side is the time to cover the distance . . . \r\n" );
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document.write( "To solve it, multiply both sides by 3*r*(r+10). You will get\r\n" );
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document.write( "    720*(r+10) - 720r = r*(r+10)\r\n" );
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document.write( "    7200 = r^2 + 10r\r\n" );
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document.write( "    r^2 + 10r - 7200\r\n" );
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document.write( "    (r-80)*(r+90) = 0\r\n" );
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document.write( "The two root of the equation are r = 80  and  r = -90,  but only positive r = 80 km/h makes sense.\r\n" );
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document.write( "ANSWER. The original speed was  80 kilometers per hour.\r\n" );
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document.write( "CHECK.    = 3 hours;    =  hours = 2 hours and 40 minutes;   the difference is  20 minutes.   ! Correct !\r\n" );
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\n" ); document.write( "\n" ); document.write( "Using \"time\" equation is the STANDARD way to solve such problems.\r
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\n" ); document.write( "\n" ); document.write( "From this solution, learn on how to write, how to use and how to solve a \"time\" equation.\r
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\n" ); document.write( "\n" ); document.write( "To see many other similar solved problems, look into the lessons\r
\n" ); document.write( "\n" ); document.write( "    - Had a car move faster it would arrive sooner\r
\n" ); document.write( "\n" ); document.write( "    - How far do you live from school? \r
\n" ); document.write( "\n" ); document.write( "    - Earthquake waves \r
\n" ); document.write( "\n" ); document.write( "    - Time equation: HOW TO use, HOW TO write and HOW TO solve it \r
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