document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1156715>Question 1156715</A>: <I><SPAN STYLE=\"word-break: break-all;\"> How long will it take a sample of radioactive substance to decay to half of its original​ amount, if it decays according to the function <BR>\n" );
document.write( "​A(t)=800e^-.215t<BR>\n" );
document.write( "where t is the time in​ years? Round your answer to the nearest hundredth year </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #779468 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=779468\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> A+Aoe^(-215t)<BR>\n" );
document.write( "but A= (1/2)A0<BR>\n" );
document.write( "so 1/2=e^(-.215t)<BR>\n" );
document.write( "ln of both sides to get rid of e<BR>\n" );
document.write( "-ln 2 (because it is ln1-ln2, and ln1 is 0)=-.215t<BR>\n" );
document.write( "negative signs go away<BR>\n" );
document.write( "t=3.22 years </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );