Algebra.Com's Answer #816787 by ikleyn(52839)![\"\"](\"/images/stars/stars-13.gif\")  
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document.write( "The distance between two cities A and B is 140 km. A car driving from A to B left at the
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document.write( "same time as a car driving from B to A. The cars met after one hour, then the first car reached
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document.write( "city B 35 minutes later than the second car reached city A. Find the speed of the car from city A to B.
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document.write( "Let \"a\" be the speed of the car A, in km/h;\r\n" );
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document.write( "let \"b\" be the speed of the car B, in km/h.\r\n" );
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document.write( "Then you have these two equation\r\n" );
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document.write( " a + b = 140 kilometers (1) (The cars met after one hour)\r\n" );
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document.write( "  -  =  of an hour (2) (first car reached city B 35 minutes later than the second car reached city A)\r\n" );
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document.write( "From the first equation, express b = 140-a and substitute it into the second equation. You will get then\r\n" );
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document.write( "  - =  \r\n" );
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document.write( "  -  =  \r\n" );
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document.write( "At this point, I just can to guess the solution MENTALLY : a = 60 km/h.\r\n" );
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document.write( "An alternative way is to reduce the last equation to the standard quadratic equation form and solve it formally.\r\n" );
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document.write( "ANSWER. The speed of the car A is 60 km/h.\r\n" );
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document.write( "CHECK. a) the speed of the car B is then 140-60 = 80 km/h.\r\n" );
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document.write( " b) the time equation (2) is then  -  =  -  =  = = = 35 minutes.\r\n" );
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document.write( " ! Correct !\r\n" );
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document.write( "Solved.\r
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