document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=729995>Question 729995</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Radioactive radium has a half-life of 1580 years.\r<BR>\n" );
document.write( "\n" );
document.write( "    A) (3 pts)  Find the rate (constant) of decay.\r<BR>\n" );
document.write( "\n" );
document.write( "    B) (4 pts)  How long will it take for 80% of a quantity of radioactive radium to decay (to a level of 20% of the original amount)?<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #446338 by </B><A HREF=/tutors/aboutme.mpl?userid=josgarithmetic><B>josgarithmetic(39621)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=josgarithmetic><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=446338\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Let A = amount<BR>\n" );
document.write( "let I = initial amount<BR>\n" );
document.write( "let t = time in years<BR>\n" );
document.write( "General decay eqaution, <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=A=I%2Ae%28-kt%29 ALIGN=MIDDLE  ALT=\"A=I%2Ae%28-kt%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "Starting at any I, half life of 1580 years makes <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%281%2F2%29%2AI=I%2Ae%5E%28-k%2A1580%29 ALIGN=MIDDLE  ALT=\"%281%2F2%29%2AI=I%2Ae%5E%28-k%2A1580%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >,<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=1%2F2=e%5E%28-k%2A1580%29 ALIGN=MIDDLE  ALT=\"1%2F2=e%5E%28-k%2A1580%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "Find k.<BR>\n" );
document.write( "...<BR>\n" );
document.write( ". </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );