document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=187395>Question 187395</A>: <I><SPAN STYLE=\"word-break: break-all;\"> After 13 years, 2.1 pounds of radioactive material remains from a 7 pound sample. What is the half-life of this material? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #140469 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=140469\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> After 13 years, 2.1 pounds of radioactive material remains from a 7 pound sample. What is the half-life of this material?<BR>\n" );
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document.write( "A(t) = A(0)(1/2)^(13/h)t<BR>\n" );
document.write( "2.1 = 7 (1/2)^(13/h)t<BR>\n" );
document.write( "0.3 = (1/2)^(13/h)<BR>\n" );
document.write( "Take the log to get:<BR>\n" );
document.write( "(13/h)log(0.5) = log(0.3)<BR>\n" );
document.write( "(13/h) = [log(0.3)]/[log(0.5)]<BR>\n" );
document.write( "13/h = 1.7370<BR>\n" );
document.write( "h = 13/1.7370<BR>\n" );
document.write( "h = 7.4843 years (this is the half-life of the material)<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );