document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=322700>Question 322700</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I wasn't sure what \"type\" of problem to put this under so hopefully you can help me.  <BR>\n" );
document.write( "Question: Suppose that a 50 million gallon contamination is reduced by 20% every year.  How long will it take to have only 100,000 gallons of oil contamination left in the Gulf? I am not sure how to figure this out.<BR>\n" );
document.write( "Thank you for your help<BR>\n" );
document.write( "Beth </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #231008 by </B><A HREF=/tutors/aboutme.mpl?userid=galactus><B>galactus(183)</B></A><img src=\"/images/stars/stars-09.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=galactus><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=galactus><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=231008\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Since it is decreasng by 20%, then 80% or 4/5 remains and we can write\r<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=50%284%2F5%29%5Et ALIGN=MIDDLE  ALT=\"50%284%2F5%29%5Et\"   DISABLED_style= \"max-width:90%; height:auto;\" >, where t is the year.\r<BR>\n" );
document.write( "\n" );
document.write( "So we do not have such large numbers to deal with, divide by a million and let the initial amount be 50 and then 100000 would be 1/10.\r<BR>\n" );
document.write( "\n" );
document.write( "Now, set this equal to 1/10 and solve for t.\r<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=50%284%2F5%29%5Et=1%2F10 ALIGN=MIDDLE  ALT=\"50%284%2F5%29%5Et=1%2F10\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=%284%2F5%29%5Et=1%2F500 ALIGN=MIDDLE  ALT=\"%284%2F5%29%5Et=1%2F500\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=tln%284%2F5%29=ln%281%2F500%29 ALIGN=MIDDLE  ALT=\"tln%284%2F5%29=ln%281%2F500%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=t=ln%281%2F500%29%2Fln%284%2F5%29 ALIGN=MIDDLE  ALT=\"t=ln%281%2F500%29%2Fln%284%2F5%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
document.write( "\n" );
document.write( "t=27.85 years\r<BR>\n" );
document.write( "\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );