document.write( "Question 1090635: The ratio of the number of boys to the number of girls in a class of 42 pupils was 4:3 when some boys left the class the number of girls was the same as the number of boys. how many boys left the class \n" ); document.write( "

Algebra.Com's Answer #705085 by ikleyn(52782) $\"\"$ $\"About$

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document.write( "Let x = be the number of boys in the class, and y be the number of girls.\r\n" );
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document.write( "Then you have two equations:\r\n" );
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document.write( " = ,\r\n" );
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document.write( "x + y = 42.\r\n" );
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document.write( "Express x via y from the first equation: x = , and substitute it into the second equation. \r\n" );
document.write( "You will get a single equation for the unknown y:\r\n" );
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document.write( " + y = 42.\r\n" );
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document.write( "Multiply both sides by 4 and simplify.\r\n" );
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document.write( "4y + 3y = 42*3 = 126,\r\n" );
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document.write( "7y = 126, \r\n" );
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document.write( "y =  = 18.\r\n" );
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document.write( "Now x =  =  = 24.\r\n" );
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document.write( "Answer. There are 24 boys and 18 girls in the class.\r\n" );
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