document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1147320>Question 1147320</A>: <I><SPAN STYLE=\"word-break: break-all;\"> After the release of radioactive material into the atmosphere from a nuclear power plant in a country in 1987, the hay in that country was contaminated by a radioactive isotope (half life 6 days). If it is safe to feed the hay to the cows when 12% of the radioactive isotope remains, how long did the farmers need to wait to use this hay? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #768639 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=768639\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "Solve <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=.5%5Ex+=+.12 ALIGN=MIDDLE  ALT=\".5%5Ex+=+.12\"   DISABLED_style= \"max-width:90%; height:auto;\" > to find the number of half-lives it takes for the percentage to reach 12%; then multiply by the number of days in the half life to find the number of days.<br><BR>\n" );
document.write( "The half life of 6 days is presumably an approximate number; and radioactive decay is random and not \"smooth\". So an approximation for an answer should be sufficient; using exactly 6 days for the half life and exactly 12% for the remaining percentage to get an answer to 5 or 6 decimal places is unrealistic.<br><BR>\n" );
document.write( "Since .5^3 = .125 = 12.5%, the remaining percentage will be very close to 12% after 3 half lives, which is 3*6 = 18 days. </SPAN>\n" );
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