document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=165826>Question 165826</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I sent this problem several days ago with no response. The level of thorium in a sample decreases by a factor one-half every 4.2million 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 #122233 by </B><A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><B>ankor@dixie-net.com(22740)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ankor@dixie-net.com><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=ankor@dixie-net.com><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=122233\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> This same problem came up about a week ago, here is what I submitted then<BR>\n" );
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document.write( " 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?<BR>\n" );
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document.write( "The decay formula: Ao*2^(-t/h) = A<BR>\n" );
document.write( "Where:<BR>\n" );
document.write( "Ao = initial amt<BR>\n" );
document.write( "A = resulting amt<BR>\n" );
document.write( "t = time (in millions of yrs)<BR>\n" );
document.write( "h = half-life of the substance (in millions of years)<BR>\n" );
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document.write( "In this problem: let Ao = 1; A = .076<BR>\n" );
document.write( "1*2^(-t/4.2) = .076<BR>\n" );
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document.write( "ln(2^(-t/4.2)) = ln(.076); find the nat log of both sides<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=-t%2F4.2 ALIGN=MIDDLE  ALT=\"-t%2F4.2\"   DISABLED_style= \"max-width:90%; height:auto;\" >.693 = -2.577; use the log equiv of exponents<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28-.693t%29%2F4.2 ALIGN=MIDDLE  ALT=\"%28-.693t%29%2F4.2\"   DISABLED_style= \"max-width:90%; height:auto;\" > = -2.577;<BR>\n" );
document.write( "Multiply both sides by 4.2<BR>\n" );
document.write( "-.693t = -2.577 * 4.2<BR>\n" );
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document.write( "-.693t = -10.823<BR>\n" );
document.write( "t = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28-10.823%29%2F%28-.693%29 ALIGN=MIDDLE  ALT=\"%28-10.823%29%2F%28-.693%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "t = 15.6 million years old<BR>\n" );
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document.write( "Check solution on a calc enter 2^(-15.6/4.2) = .076..\r<BR>\n" );
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document.write( " </SPAN>\n" );
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