document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=33363>Question 33363</A>: <I><SPAN STYLE=\"word-break: break-all;\"> How old is a skeleton that has lost 75% of its Carbon-14?  I have NO idea how to do this problem.  Could someone help me? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #19895 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=19895\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The half-life of Carbon-14 is 5700 years<BR>\n" );
document.write( "The formula you need is <BR>\n" );
document.write( "Amount you now have= (Amount you started with)(1/2)^(t/5700)<BR>\n" );
document.write( "You want the \"Amount you now have\" to be 75% of \"Amount you started with\".<BR>\n" );
document.write( "EQUATIOn:<BR>\n" );
document.write( "Let the original amount be \"x\".<BR>\n" );
document.write( "0.75x=x(1/2)^(t/5700) where t is the number of years <BR>\n" );
document.write( "0.75=(1/2)^(t/5700)<BR>\n" );
document.write( "Take the natural log of both sides to get:<BR>\n" );
document.write( "ln(0.75)=(t/500)[ln(1/2)]<BR>\n" );
document.write( "t/5700= [ln0.75]/[ln(1/2)]<BR>\n" );
document.write( "t/5700=0.415037...<BR>\n" );
document.write( "t=2365.71 years.<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );