document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=155438>Question 155438</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 its 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 #114682 by </B><A HREF=/tutors/aboutme.mpl?userid=scott8148><B>scott8148(6628)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=scott8148><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=scott8148><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=114682\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> a formula for half-life is A=Ao(1/2)^(t/h)\r<BR>\n" );
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document.write( "A=current amount __ Ao=initial amount __ t=time __ h=half-life\r<BR>\n" );
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document.write( ".076=(.5)^(t/4.2x10^6) __ taking log __ log(.076)=(t/4.2x10^6)log(.5)\r<BR>\n" );
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document.write( "dividing by log(.5) __ [log(.076)]/[log(.5)]=t/4.2x10^6 __ multiplying by 4.2x10^6 __ {[log(.076)]/[log(.5)]}(4.2x10^6)=t\r<BR>\n" );
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document.write( "1.56x10^7=t </SPAN>\n" );
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