document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=334872>Question 334872</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Find the half life of a radioactive substance that decays by 20% in 10 years. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #239944 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=239944\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Find the half life of a radioactive substance that decays by 20% in 10 years.<BR>\n" );
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document.write( "A(t)= a*b^t<BR>\n" );
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document.write( "Given: <BR>\n" );
document.write( "0.20a = ab^10<BR>\n" );
document.write( "b^10 = 0.20<BR>\n" );
document.write( "b = 0.2^(1/10)<BR>\n" );
document.write( "====================<BR>\n" );
document.write( "Find half-life:<BR>\n" );
document.write( "(1/2)a = a*b^t<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Cancel the \"a's\" and substitute for \"b\":<BR>\n" );
document.write( "1/2 = 0.2^(t/10)<BR>\n" );
document.write( "Solve for \"t\":<BR>\n" );
document.write( "(t/10)log(0.2) = log(0.5)<BR>\n" );
document.write( "t/10 = log(0.5)/log(0.2)<BR>\n" );
document.write( "t/10 = 0.4307<BR>\n" );
document.write( "t = 4.307 years (half-life of the substance)<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( "========== <BR>\n" );
document.write( " </SPAN>\n" );
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