document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=924347>Question 924347</A>: <I><SPAN STYLE=\"word-break: break-all;\"> 320 mg of Iodine 131 is stored in a laboratory for 40 days.  At the end of this period only 10 mg of the element remains.  What is the half-life of Iodine 131? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #560770 by </B><A HREF=/tutors/aboutme.mpl?userid=josgarithmetic><B>josgarithmetic(39620)</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=560770\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Start with a general exponential decay equation and solve for for t and for k.\r<BR>\n" );
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document.write( "A generalized exponential decay equation:  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=y=b%2Ae%5E%28kt%29 ALIGN=MIDDLE  ALT=\"y=b%2Ae%5E%28kt%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > using assigned variables,<BR>\n" );
document.write( "y, amount at any time t<BR>\n" );
document.write( "b, initial amount at t=0<BR>\n" );
document.write( "k, a rate constant which will be negative<BR>\n" );
document.write( "t, passage of time in day\r<BR>\n" );
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document.write( "SOLVE THE DECAY EQUATION SYMBOLICALLY FOR THE TERM kt:<BR>\n" );
document.write( "TAKE LOGs OF BOTH SIDES, A FEW STEPS NOT SHOWN HERE BUT SHOULD STILL BE UNDERSTOOD (HOPEFULLY):<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ln%28y%29=ln%28b%29%2Bln%28e%5E%28kt%29%29 ALIGN=MIDDLE  ALT=\"ln%28y%29=ln%28b%29%2Bln%28e%5E%28kt%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ln%28y%29=ln%28b%29%2Bkt ALIGN=MIDDLE  ALT=\"ln%28y%29=ln%28b%29%2Bkt\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=kt=ln%28y%29-ln%28b%29 ALIGN=MIDDLE  ALT=\"kt=ln%28y%29-ln%28b%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=highlight_green%28kt=ln%28y%2Fb%29%29 ALIGN=MIDDLE  ALT=\"highlight_green%28kt=ln%28y%2Fb%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >; first use this to find k from the first  two sentence.  Use the green outlined equation again to find half-life. </SPAN>\n" );
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