document.write( "Question 87278: John is 12 years younger than Mary. Mery's age in 8 years will exceeed twice John's age 3 year's ago by 4 years. How old is each now? \n" ); document.write( "
Algebra.Com's Answer #63220 by Edwin McCravy(20056)\"\" \"About 
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John is 12 years younger than Mary. Mary's age in 8 years will exceeed twice
\n" ); document.write( "John's age 3 year's ago by 4 years. How old is each now?:
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document.write( "I can't tell if you are studying solving using 1 unknown or 2 unknowns.\r\n" );
document.write( "This can be done either way.  I'll do it both ways:\r\n" );
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document.write( "Using only one unknown:\r\n" );
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document.write( ">>...John is 12 years younger than Mery...<<\r\n" );
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document.write( "John's age is defined in terms of Mary's age, and whenever possible we\r\n" );
document.write( "like to define in terms of x, so let Mary's age = x, then\r\n" );
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document.write( "John's age now = Mary's age now minus 12, or\r\n" );
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document.write( "John's age = x - 12\r\n" );
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document.write( ">>...Mary's age in 8 years will exceeed twice John's age 3 year's ago by 4 years...<<\r\n" );
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document.write( "That is to say:\r\n" );
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document.write( ">>...Mary's age in 8 years equals twice John's age 3 years ago PLUS 4...<<\r\n" );
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document.write( "Mary's age in 8 years = Mary's age now + 8 \r\n" );
document.write( "Mary's age in 8 years = x + 8\r\n" );
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document.write( "John's age 3 years ago = John's age now - 3\r\n" );
document.write( "John's age 3 years ago = (x - 12) - 3 = x - 12 - 3 = x - 15\r\n" );
document.write( "Twice John's age 3 years ago = 2(x - 15) = 2x - 30\r\n" );
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document.write( "x + 8 = (2x - 30) + 4\r\n" );
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document.write( "Solve that and get x = 34\r\n" );
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document.write( "So Mary is 34 and John is 12 years younger or 34-12 = 22\r\n" );
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document.write( "Using two unknowns:\r\n" );
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document.write( "John is 12 years younger than Mary. \r\n" );
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document.write( "J = M - 12\r\n" );
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document.write( "Mary's age in 8 years will exceeed twice John's\r\n" );
document.write( " age 3 year's ago by 4 years.\r\n" );
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document.write( "M + 8 = 2(J - 3) + 4\r\n" );
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document.write( "So you have the system of two equations in two unknowns.\r\n" );
document.write( "Simplify the second and use substitution\r\n" );
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document.write( "J = M - 12\r\n" );
document.write( "M + 8 = 2(J - 3) + 4\r\n" );
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document.write( "and you will get J = 22 and M = 34.\r\n" );
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document.write( "Edwin
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