document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=165660>Question 165660</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The level of thorium in a sample decreases by a factor of one-half every 4.2 million years. A meteorite is discovered to have only 7.6% of it's original thorium remaining. How old is the meteorite? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #122125 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=122125\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The level of thorium in a sample decreases by a factor of one-half every 4.2 million years. A meteorite is discovered to have only 7.6% of it's original thorium remaining. How old is the meteorite?<BR>\n" );
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document.write( "A(t) = Ao(1/2)^(t/4.2 million)<BR>\n" );
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document.write( "0.076Ao = Ao(1/2)^(t/4.2 million)<BR>\n" );
document.write( "(1/2)^(t/4.2 million) = 0.076<BR>\n" );
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document.write( "Take the log of both sides to get:<BR>\n" );
document.write( "(t/4.2 million)*(log(1/2)) = log 0.076<BR>\n" );
document.write( "t/4.2 million = [log(0.076)]/[log(1/2)] = 3.717856...<BR>\n" );
document.write( "t = 3.717856...* 4.2 million<BR>\n" );
document.write( "t = 15.615 million years<BR>\n" );
document.write( "============================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );