document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1136372>Question 1136372</A>: <I><SPAN STYLE=\"word-break: break-all;\"> An unknown radioactive element decays into non-radioactive substances. In 560 days the radioactivity of a sample decreases by 51 percent. \r<BR>\n" );
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document.write( "(a) What is the half-life of the element? <BR>\n" );
document.write( "half-life:  <BR>\n" );
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document.write( "(b) How long will it take for a sample of 100 mg to decay to 47 mg? <BR>\n" );
document.write( "time needed: <BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #754157 by </B><A HREF=/tutors/aboutme.mpl?userid=josgarithmetic><B>josgarithmetic(39617)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=josgarithmetic><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=754157\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=49=100%2Ae%5E%28-560k%29 ALIGN=MIDDLE  ALT=\"49=100%2Ae%5E%28-560k%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >------first step is to find the value of k.\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=0.49=e%5E%28-560k%29 ALIGN=MIDDLE  ALT=\"0.49=e%5E%28-560k%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=ln%280.49%29=-560k ALIGN=MIDDLE  ALT=\"ln%280.49%29=-560k\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=k=-ln%280.49%29%2F560 ALIGN=MIDDLE  ALT=\"k=-ln%280.49%29%2F560\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=k=0.0012738 ALIGN=MIDDLE  ALT=\"k=0.0012738\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "MODEL:  <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=highlight_green%28y=pe%5E%28-0.0012738x%29%29 ALIGN=MIDDLE  ALT=\"highlight_green%28y=pe%5E%28-0.0012738x%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "Note that the half life will be very close to 560 days.<BR>\n" );
document.write( "More like 546 days.\r<BR>\n" );
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