document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1026381>Question 1026381</A>: <I><SPAN STYLE=\"word-break: break-all;\"> If 250 mg of a radioactive element decays to 230 mg in 12 hours, find the half-life of the element. (Round your answer to the nearest whole number.)<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 #641919 by </B><A HREF=/tutors/aboutme.mpl?userid=robertb><B>robertb(5830)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=robertb><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=robertb><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=641919\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> For exponential decay/growth the basic model is <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=P=P%5B0%5De%5E%28rt%29+=+250e%5E%28rt%29 ALIGN=MIDDLE  ALT=\"P=P%5B0%5De%5E%28rt%29+=+250e%5E%28rt%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >.\r<BR>\n" );
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document.write( "After 12 hours, the equation becomes <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=230+=+250e%5E%2812r%29 ALIGN=MIDDLE  ALT=\"230+=+250e%5E%2812r%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=0.92+=+e%5E%2812r%29 ALIGN=MIDDLE  ALT=\"0.92+=+e%5E%2812r%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > ==> ln0.92 = 12r, or <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=r+=+ln0.92%2F12 ALIGN=MIDDLE  ALT=\"r+=+ln0.92%2F12\"   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=P=P%5B0%5De%5E%28rt%29+=+250e%5E%28rt%29+=+250e%5E%28tln0.92%2F12%29+=+250%2A0.92%5E%28t%2F12%29 ALIGN=MIDDLE   DISABLED_style= \"max-width:90%; height:auto;\" >, or\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=P+=+250%2A.92%5E%28t%2F12%29 ALIGN=MIDDLE  ALT=\"P+=+250%2A.92%5E%28t%2F12%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >.<BR>\n" );
document.write( "To find the half-life set P=125 (half of 250.)\r<BR>\n" );
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document.write( "==> <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=125+=+250%2A.92%5E%28t%2F12%29 ALIGN=MIDDLE  ALT=\"125+=+250%2A.92%5E%28t%2F12%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >.<BR>\n" );
document.write( "==> <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=0.5+=+0.92%5E%28t%2F12%29 ALIGN=MIDDLE  ALT=\"0.5+=+0.92%5E%28t%2F12%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >  ==> <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=t+=+-12log2%2Flog0.92 ALIGN=MIDDLE  ALT=\"t+=+-12log2%2Flog0.92\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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document.write( "==> t = 99.8, or 100 hours, rounded off to the nearest whole number.\r<BR>\n" );
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