document.write( "Question 1161375: 1) Suppose you want to have $500,000 for retirement. Your account earns 9% interest compounded monthly. If you deposit $200 at the end of each month, how long will it take you to reach your goal? Round to the nearest year.\r
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Algebra.Com's Answer #784897 by ikleyn(52781)\"\" \"About 
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document.write( "The formula for an Ordinary Annuity saving account compounded monthly  is\r\n" );
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document.write( "    FV = \"P%2A%28%281%2Br%2F12%29%5En-1%29%2F%28%28r%2F12%29%29\"\r\n" );
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document.write( "where FV is the future value, P is the annual payment at the end of each year, n is the number of monthly deposits (of months).\r\n" );
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document.write( "So, we need to find \" n \" from the equation\r\n" );
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document.write( "    \"%28%281%2B0.09%2F12%29%5En-1%29%2F%28%280.09%2F12%29%29\" = \"FV%2FP\" = \"500000%2F200\" = 2500,  which is the same as\r\n" );
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document.write( "    \"%28%281%2B0.0075%29%5En-1%29%2F0.0075\" = 2500.\r\n" );
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document.write( "Rewrite it in this form\r\n" );
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document.write( "    \"1.0075%5En-1\" = 0.0075*2500,\r\n" );
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document.write( "    \"%281.0075%29%5En\" = 1 + 0.0075*2500 = 19.75.\r\n" );
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document.write( "Take the logarithm base 10 of both sides\r\n" );
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document.write( "    n*log(1.0075) = log(19.75)\r\n" );
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document.write( "and calculate  \r\n" );
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document.write( "     n = \"log%28%2819.75%29%29%2Flog%28%281.0075%29%29\" = 399.2  months = 400 months (rounded to the nearest greater integer value) = 33 years and 4 months.   ANSWER\r\n" );
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document.write( "CHECK.  \"200%2A%28%281.0075%5E399-1%29%2F0.0075%29\" = 499042.54, which is slightly less than 500000;\r\n" );
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document.write( "        \"200%2A%28%281.0075%5E400-1%29%2F0.0075%29\" = 502985.38, which is slightly greater than 500000.\r\n" );
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\n" ); document.write( "\n" ); document.write( "On ordinary annuity saving plan,  see my lessons in this site \r
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\n" ); document.write( "\n" ); document.write( "    - Ordinary Annuity saving plans and geometric progressions\r
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