document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=253874>Question 253874</A>: <I><SPAN STYLE=\"word-break: break-all;\"> beryllium-11 decomposes into boron-11 with a half life of 13.8 seconds.  How long will it take 240 g of beryllium-11 to decompose into 7.5g of beryllium-11? \r<BR>\n" );
document.write( "\n" );
document.write( "based on the forumula provided in the text book C(t)=C(0)2e^-t/h\r<BR>\n" );
document.write( "\n" );
document.write( "where C(0) = 240, C(t)=7.5 ,h=13.8\r<BR>\n" );
document.write( "\n" );
document.write( "7.5/240=2e^-t/13.8\r<BR>\n" );
document.write( "\n" );
document.write( "this was a s far as i got </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #186249 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=186249\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> beryllium-11 decomposes into boron-11 with a half life of 13.8 seconds.<BR>\n" );
document.write( " How long will it take 240 g of beryllium-11 to decompose into 7.5g of beryllium-11?<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Here is what it should be then:<BR>\n" );
document.write( "2^(-t/13.8) = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=7.5%2F240 ALIGN=MIDDLE  ALT=\"7.5%2F240\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "2^(-t/13.8) = .03125<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Find the natural log of both sides<BR>\n" );
document.write( "ln(2^(-t/13.8)) = ln(.03125)<BR>\n" );
document.write( ":<BR>\n" );
document.write( "log equiv of exponents<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=-t%2F13.8 ALIGN=MIDDLE  ALT=\"-t%2F13.8\"   DISABLED_style= \"max-width:90%; height:auto;\" >*ln(2) = ln(.03125)<BR>\n" );
document.write( ":<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=-t%2F13.8 ALIGN=MIDDLE  ALT=\"-t%2F13.8\"   DISABLED_style= \"max-width:90%; height:auto;\" >(.693) = -3.4657<BR>\n" );
document.write( ":<BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=-.693t%2F13.8 ALIGN=MIDDLE  ALT=\"-.693t%2F13.8\"   DISABLED_style= \"max-width:90%; height:auto;\" > = -3.4657<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Multiply both sides by -13.8<BR>\n" );
document.write( ".693t = -13.8 * -3.4657<BR>\n" );
document.write( "693t = +47.827 seconds<BR>\n" );
document.write( "t = <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%2847.827%29%2F%28.693%29 ALIGN=MIDDLE  ALT=\"%2847.827%29%2F%28.693%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "t = 69 sec<BR>\n" );
document.write( ":<BR>\n" );
document.write( ":<BR>\n" );
document.write( "Check on a calc: enter 240*2^(-69/13.8) = 7.500<BR>\n" );
document.write( "  </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );