document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=236324>Question 236324</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Radioactive strontium 90Sr has been deposited in a large field by acid rain. If sufficient amounts make their way through the food chain to humans, bone cancer can result. It has been determined that the radioactivity level in the field is 1.7 times the save level S. 90Sr decyas according to the formula <BR>\n" );
document.write( "A(t)=Aoe^-0.0239t<BR>\n" );
document.write( "where Ao is the amount curretly in the field and t is the time in years. How many years will it take until the field is contaminated.  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #173974 by </B><A HREF=/tutors/aboutme.mpl?userid=nerdybill><B>nerdybill(7384)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=nerdybill><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=nerdybill><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=173974\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Radioactive strontium 90Sr has been deposited in a large field by acid rain. If sufficient amounts make their way through the food chain to humans, bone cancer can result. It has been determined that the radioactivity level in the field is 1.7 times the save level S. 90Sr decyas according to the formula<BR>\n" );
document.write( "A(t)=Aoe^-0.0239t<BR>\n" );
document.write( "I think they want to know when the fields  will be safe.<BR>\n" );
document.write( ".<BR>\n" );
document.write( "A(t)=Aoe^-0.0239t<BR>\n" );
document.write( "Let x = initial amount of strontium<BR>\n" );
document.write( "then<BR>\n" );
document.write( "x/1.7 = A(t)<BR>\n" );
document.write( ".<BR>\n" );
document.write( "x/1.7 = xe^-0.0239t<BR>\n" );
document.write( "1/1.7 = e^-0.0239t<BR>\n" );
document.write( "ln(1/1.7) = -0.0239t<BR>\n" );
document.write( "ln(1/1.7) /-0.0239 = t<BR>\n" );
document.write( "22.2 years = t (years before the strontium decays to safe levels)<BR>\n" );
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