document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1092511>Question 1092511</A>: <I><SPAN STYLE=\"word-break: break-all;\">  Sean is 20 and his brother is 12 how many years ago was sean three times as old as his brother  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #707134 by </B><A HREF=/tutors/aboutme.mpl?userid=DrSteve><B>DrSteve(7)</B></A><img src=\"/images/stars/stars-05.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=DrSteve><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=DrSteve><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=707134\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> I love problems like this!  They're like wacky puzzles!\r<BR>\n" );
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document.write( "So lets set this one up:\r<BR>\n" );
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document.write( "what number, subtracted from BOTH THEIR AGES, will result in a number that makes Sean's age three times his brother's?\r<BR>\n" );
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document.write( "let's call Sean \"S\" and his brother \"B\" for the general equation, then we'll solve it.   The number of years we're subtracting we'll just call \"x\".\r<BR>\n" );
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document.write( "S-x = 3(B - x)\r<BR>\n" );
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document.write( "in other words, Sean's age minus a number, is equal to 3 times Brother's age minus the same number.\r<BR>\n" );
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document.write( "We know Sean and Brother's ages, though, so let's plug them in!\r<BR>\n" );
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document.write( "20 - x = 3(12 - x)\r<BR>\n" );
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document.write( "expanding the parenthetical gives us\r<BR>\n" );
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document.write( "20 - x = 36 - 3x\r<BR>\n" );
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document.write( "now add x to both sides\r<BR>\n" );
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document.write( "20 = 36 - 2x\r<BR>\n" );
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document.write( "subtract 36 from both sides\r<BR>\n" );
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document.write( "-16 = -2x\r<BR>\n" );
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document.write( "divide both sides by -2\r<BR>\n" );
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document.write( "8 = x\r<BR>\n" );
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document.write( "...which is your answer!\r<BR>\n" );
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document.write( "You can check it thusly:\r<BR>\n" );
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document.write( "20 - 8 = 12<BR>\n" );
document.write( "12 - 8 = 4\r<BR>\n" );
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document.write( "12/4 = 3  and there you go! </SPAN>\n" );
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