document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1190047>Question 1190047</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A sample of a radioactive substance has an initial mass of 31.9 mg. This substance follows a continuous exponential decay model<BR>\n" );
document.write( "and has a half-life of 9 minutes.\r<BR>\n" );
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document.write( "(a) Let t be the time (in minutes) since the start of the experiment, and<BR>\n" );
document.write( "let y be the amount of the substance at time t.<BR>\n" );
document.write( "Write a formula relating y to t.<BR>\n" );
document.write( "Use exact expressions to fill in the missing parts of the formula.<BR>\n" );
document.write( "Do not use approximations.\r<BR>\n" );
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document.write( "(b) How much will be present in 14 minutes?<BR>\n" );
document.write( "Do not round any intermediate computations, and round your<BR>\n" );
document.write( "answer to the nearest tenth.<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #821605 by </B><A HREF=/tutors/aboutme.mpl?userid=ikleyn><B>ikleyn(52809)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ikleyn><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=ikleyn><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=821605\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> .<BR>\n" );
document.write( "<PRE STYLE=\"white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;\">\r\n" );
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document.write( "The formula is  \r\n" );
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document.write( "    y = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=31.9%2A%281%2F2%29%5E%28t%2F9%29 ALIGN=MIDDLE  ALT=\"31.9%2A%281%2F2%29%5E%28t%2F9%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >.\r\n" );
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document.write( "Notice that 31.9 is the initial amount at the beginning  (t= 0).\r\n" );
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document.write( "The denominator \"9\" in the index of the exponential function is the half-life time 9 minutes.\r\n" );
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document.write( "t is the current time in minutes.\r\n" );
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document.write( "To calculate remaining mass at t= 14 minutes,  substitute t= 14 into the formula and compute.\r\n" );
document.write( "</PRE>\r<BR>\n" );
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document.write( "On radioactive decay, &nbsp;see the lesson\r<BR>\n" );
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document.write( "&nbsp;&nbsp;&nbsp;&nbsp;- <A  rel=nofollow HREF=https://www.algebra.com/algebra/homework/logarithm/Radioactive-decay-problems.lesson>Radioactive decay problems</A> \r<BR>\n" );
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document.write( "in this site.\r<BR>\n" );
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document.write( "You will find many similar &nbsp;(and different) &nbsp;solved problems there.\r<BR>\n" );
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document.write( "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Use this lesson as your handbook, &nbsp;textbook, &nbsp;guide, &nbsp;tutorials, and &nbsp;(free of charge) &nbsp;home teacher.\r<BR>\n" );
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document.write( "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Learn the subject from there once and for all.\r<BR>\n" );
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document.write( "Also, &nbsp;you have this free of charge online textbook in &nbsp;ALGEBRA-I &nbsp;in this site\r<BR>\n" );
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document.write( "&nbsp;&nbsp;&nbsp;&nbsp;- <A  rel=nofollow HREF=https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson>ALGEBRA-I - YOUR ONLINE TEXTBOOK</A>.\r<BR>\n" );
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document.write( "The referred lesson is the part of this online textbook under the topic \"<U>Logarithms</U>\".\r<BR>\n" );
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document.write( "Save the link to this online textbook together with its description\r<BR>\n" );
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document.write( "Free of charge online textbook in ALGEBRA-I<BR>\n" );
document.write( "https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson\r<BR>\n" );
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document.write( "to your archive and use it when it is needed.\r<BR>\n" );
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document.write( " </SPAN>\n" );
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