document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=25686>Question 25686</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Find the exponential decay function for a radioactive material that has a half-life of 1234 years. How long will it take until only 10% of the material remains?\r<BR>\n" );
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document.write( "I'm just having a problem setting up this problem. Any help you can give will be greatly appreciated. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #13796 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=13796\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Formula: A=P(1/2)^(t/1234)<BR>\n" );
document.write( "A is the amount you have after some years.<BR>\n" );
document.write( "P is the amount you started with.<BR>\n" );
document.write( "t is the number of years since the start time.<BR>\n" );
document.write( "You want A=10%(p)= 0.1P<BR>\n" );
document.write( "So, you have 0.1P=P(1/2)^(t/1234)<BR>\n" );
document.write( "0.1=2^(-t/1234)<BR>\n" );
document.write( "Take the ln of both sides to get:<BR>\n" );
document.write( " ln(0.1)= (-t/1234)(ln 2)<BR>\n" );
document.write( "  t=[-1234{ln 0.1)/(ln 2)]<BR>\n" );
document.write( "I don't have a calculator with me so I will leave<BR>\n" );
document.write( "the calculating to you.\r<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
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