document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=973066>Question 973066</A>: <I><SPAN STYLE=\"word-break: break-all;\"> How do you do this decay problem?\r<BR>\n" );
document.write( "\n" );
document.write( "The radioactive isotope 123I, used in nuclear imaging, decays continuously at a rate of 5.25% per hour.<BR>\n" );
document.write( "(a) Approximate the percentage remaining of any initial amount after 26.4 hours.<BR>\n" );
document.write( "(b) What is the half-life of 123I?\r<BR>\n" );
document.write( "\n" );
document.write( "For part a I think the formula for that is A(t)=A*e^(kt). The problem that I'm having with this is that I don't know the initial amount (A). Here are the variables:\r<BR>\n" );
document.write( "\n" );
document.write( "A=?<BR>\n" );
document.write( "k=?<BR>\n" );
document.write( "t=26.4\r<BR>\n" );
document.write( "\n" );
document.write( "It seems like it's asking what (k) would be but I don't know how to solve for (k) without knowing the initial amount (A). I think I may be looking at it wrong. Any help on this one would be appreciated. I know how to do part b but I need to know how to do part a first before I can do b.\r<BR>\n" );
document.write( "\n" );
document.write( "Thank you!!\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\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 #595330 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=595330\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Retention is  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=100-5.25=94.75 ALIGN=MIDDLE  ALT=\"100-5.25=94.75\"   DISABLED_style= \"max-width:90%; height:auto;\" > percent each hour.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "Starting with quantity 1, Using the model,<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=0.9475=1%2Ae%5E%28k%2A1%29 ALIGN=MIDDLE  ALT=\"0.9475=1%2Ae%5E%28k%2A1%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=0.9475=e%5Ek ALIGN=MIDDLE  ALT=\"0.9475=e%5Ek\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ln%280.9475%29=k%2A1 ALIGN=MIDDLE  ALT=\"ln%280.9475%29=k%2A1\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=highlight%28k=ln%280.9475%29%29 ALIGN=MIDDLE  ALT=\"highlight%28k=ln%280.9475%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > and the model is more specifically <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=highlight_green%28A%28t%29=A%2Ae%5E%28-0.05393t%29%29 ALIGN=MIDDLE  ALT=\"highlight_green%28A%28t%29=A%2Ae%5E%28-0.05393t%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >.\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "HALF-LIFE\r<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%281%2F2%29=1%2Ae%5E%28-0.05393t%29 ALIGN=MIDDLE  ALT=\"%281%2F2%29=1%2Ae%5E%28-0.05393t%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ln%281%2F2%29=-0.05393%2At%2Aln%28e%29 ALIGN=MIDDLE  ALT=\"ln%281%2F2%29=-0.05393%2At%2Aln%28e%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=t=ln%281%2F2%29%2F%28-0.05393%29 ALIGN=MIDDLE  ALT=\"t=ln%281%2F2%29%2F%28-0.05393%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=highlight%28t=12.9%29 ALIGN=MIDDLE  ALT=\"highlight%28t=12.9%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > hours </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );