document.write( "Question 1083856: In 9 years time a mother will be twice as old as her son. Three years ago she was four times as old as her son. Find their present age.\r
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Algebra.Com's Answer #697908 by ikleyn(52788) $\"\"$ $\"About$

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document.write( "Let M be the mother's present age, and S be the son's present age.\r\n" );
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document.write( "Then in 9 years  \r\n" );
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document.write( "M + 9 = 2*(S+9).   (1)\r\n" );
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document.write( "Three years ago \r\n" );
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document.write( "M - 3 = 4*(S-3).   (2)\r\n" );
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document.write( "So, you have these two equations\r\n" );
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document.write( "M + 9 = 2S + 18    (3)\r\n" );
document.write( "M - 3 = 4S - 12.   (4)\r\n" );
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document.write( "Subtract equation (3) from equation (4) (both sides). You will get\r\n" );
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document.write( "-3 - 9 = 2S -12 - 18,   or\r\n" );
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document.write( "-12 = 2S - 30,   or\r\n" );
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document.write( "2S = 30 - 12 = 18,   which implies   S =  = 9.\r\n" );
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document.write( "Thus the son's present age is 9 years. \r\n" );
document.write( "Then that of the mother is 2*(S+9) - 9 = 2(9+9) - 9 = 2*18-9 = 27.  (from the equation (1)).\r\n" );
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document.write( "Check.  You need to check the equation (2).\r\n" );
document.write( "        M - 3 = 27 - 3 = 24.   S - 3 = 9 - 3 = 6.   24 = 4*6.   Correct.\r\n" );
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\n" ); document.write( "\n" ); document.write( "Answer. Mother's present age is 27 years. The son's present age is 9 years.\r
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\n" ); document.write( "\n" ); document.write( "There is a bunch of lessons on age word problems \r
\n" ); document.write( "\n" ); document.write( "    - Age problems and their solutions\r
\n" ); document.write( "\n" ); document.write( "    - A fresh formulation of a traditional age problem\r
\n" ); document.write( "\n" ); document.write( "    - Really intricate age word problem\r
\n" ); document.write( "\n" ); document.write( "    - Selected age word problems from the archive\r
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\n" ); document.write( "\n" ); document.write( "Read them and become an expert in solving age problems.\r
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\n" ); document.write( "\n" ); document.write( "Also, you have this free of charge online textbook in ALGEBRA-I in this site\r
\n" ); document.write( "\n" ); document.write( "    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.\r
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\n" ); document.write( "\n" ); document.write( "The referred lessons are the part of this online textbook under the topic \"Age word problems\".\r
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