document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1192687>Question 1192687</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Wood deposits recovered from an archaeological site contain 13% of the C-14 they originally contained. How long ago did the tree from which the wood was obtained die? (Assume the half life of carbon-14 is 5,730 years. Round your answer to the nearest whole number.) </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #824604 by </B><A HREF=/tutors/aboutme.mpl?userid=Boreal><B>Boreal(15235)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Boreal><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=Boreal><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=824604\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Nf=Noe^(-kt)<BR>\n" );
document.write( "(1/2)=e^(-kt) for half life<BR>\n" );
document.write( "ln(1/2)=(-5730k)<BR>\n" );
document.write( "-0.693=-5730k<BR>\n" );
document.write( "k=0.0001210<BR>\n" );
document.write( "now Nf/No=0.13<BR>\n" );
document.write( "so 0.13=e^(-0.0001210t)<BR>\n" );
document.write( "ln both sides to remove e<BR>\n" );
document.write( "-2.040=-0.0001210t<BR>\n" );
document.write( "t=16,861 years.<BR>\n" );
document.write( "13% is not quite 3 half lives (12.5% is), which is 17,190 years, so the answer makes sense. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );