document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1199250>Question 1199250</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The half-life of a radioactive substance is one hundred twenty-five days. How many days will it take for eighty-two percent of the substance to decay?\r<BR>\n" );
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document.write( "A. 180<BR>\n" );
document.write( "B. 367<BR>\n" );
document.write( "C. 275<BR>\n" );
document.write( "D. 310<BR>\n" );
document.write( "E. 532<BR>\n" );
document.write( "F. 426 </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #833044 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13200)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=greenestamps><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=greenestamps><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=833044\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "The required calculations are easier if you use the given information to find the number of half-lives and then multiply that result by the number of days in the half-life to find the number of days.<br><BR>\n" );
document.write( "82% decayed means 18% remains.<br><BR>\n" );
document.write( "Given multiple choice answers, by far the easiest way to find the answer is to do some rough estimation. After 2 half-lives, 25% remains; after 3 half-lives, 12.5% remains.  Since we want 18% remaining, the number of half-lives should be about 2.5.  2.5 times 125 days is about 312 days; only answer choice D is close to that.<br><BR>\n" );
document.write( "For detailed calculations....<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%28.5%29%5Ex=0.18 ALIGN=MIDDLE  ALT=\"%28.5%29%5Ex=0.18\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x%2Alog%28%28.5%29%29=log%28%280.18%29%29 ALIGN=MIDDLE  ALT=\"x%2Alog%28%28.5%29%29=log%28%280.18%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x=log%28%280.18%29%29%2Flog%28%28.5%29%29 ALIGN=MIDDLE  ALT=\"x=log%28%280.18%29%29%2Flog%28%28.5%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 2.474 to 3 decimal places<br><BR>\n" );
document.write( "2.474*125 = 309 to the nearest whole number.<br><BR>\n" );
document.write( "ANSWER: D 310 days<br><BR>\n" );
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