document.write( "Question 1173788: Sue travels an average driving speed of 20km/h faster than john. she can drive 810km in the same time john can drive 720km. what is each of there speed in km/h and time in h \n" ); document.write( "

Algebra.Com's Answer #799095 by ikleyn(52909) $\"\"$ $\"About$

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document.write( "Let x = John' speed, in km/h.\r\n" );
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document.write( "Then the Sue speed is (x+20) km/h.\r\n" );
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document.write( "From the condition, you have this \"time\" equation\r\n" );
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document.write( "     = ,\r\n" );
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document.write( "or, dividing by 90 both sides\r\n" );
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document.write( "     = .\r\n" );
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document.write( "Cross multiply\r\n" );
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document.write( "    9x = 8(x+20)\r\n" );
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document.write( "and solve\r\n" );
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document.write( "    9x = 8x + 160\r\n" );
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document.write( "    9x - 8x = 160\r\n" );
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document.write( "       x    = 160  km/h for John,\r\n" );
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document.write( "and           160+20 = 180 km/h for Sue.\r\n" );
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