document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1072367>Question 1072367</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A tank of water is contaminated with 70 pounds of salt. In order to bring the salt concentration down to a level consistent with EPA standards, clean water is being piped into the tank, and the well-mixed overflow is being collected for removal to a toxic-waste site. The result is that at the end of each hour there is 19% less salt in the tank than at the beginning of the hour. Let S = S(t) denote the number of pounds of salt in the tank t hours after the flushing process begins.<BR>\n" );
document.write( "(a) Give a formula for S<BR>\n" );
document.write( "- 70(81^t)<BR>\n" );
document.write( "(b) In order to meet EPA standards, there can be no more than 3 pounds of salt in the tank. How long must the process continue before EPA standards are met?<BR>\n" );
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document.write( "(c) Suppose this cleanup procedure costs $8000 per hour to operate. How much does it cost to reduce the amount of salt from 70 pounds to 3 pounds? (Round your answer to the nearest dollar.<BR>\n" );
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document.write( "(d) How much does it cost to reduce the amount of salt from 3 pounds to 0.1 pound? (Round your answer to the nearest whole dollar.)<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 #687292 by </B><A HREF=/tutors/aboutme.mpl?userid=jorel1380><B>jorel1380(3719)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=jorel1380><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=jorel1380><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=687292\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> At t(0) you have 70 lbs of salt in the tank. Since each hour of the process removes 19% of the salt solution, this leaves you with 81% of the salt you had to begin with. So the formula for the process would be:\r<BR>\n" );
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document.write( "a)Salt=70 lbs. x .81^t where t is the amount of time, in hours, that the process has been running.\r<BR>\n" );
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document.write( "b)To get down to 3 lbs of salt we need:<BR>\n" );
document.write( "3=70 x .81^t<BR>\n" );
document.write( ".81^t=70/3<BR>\n" );
document.write( "t=approximately 14.95 hours\r<BR>\n" );
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document.write( "c)$8000/houe x 14.95 hours=  $119584.95\r<BR>\n" );
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document.write( "d).1=3 x .81^t<BR>\n" );
document.write( "t=16.41<BR>\n" );
document.write( "$8000 x 16.41=$131280 to reduce the salt from 3 lbs. to .1 lbs.  </SPAN>\n" );
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