document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=73053>Question 73053</A>: <I><SPAN STYLE=\"word-break: break-all;\"> I have only 3 questions like this\r<BR>\n" );
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document.write( "The amount of a radioactive tracer remaining after t days is given by A = AO e-0.18t, where A0 is the starting amount at the beginning of the time period. How much should be acquired now to have 40 grams remaining after 3 days?\r<BR>\n" );
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document.write( "47.9\r<BR>\n" );
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document.write( "48.8\r<BR>\n" );
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document.write( "61.6\r<BR>\n" );
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document.write( "68.6\r<BR>\n" );
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document.write( "please teach me through this. Thank you </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #52310 by </B><A HREF=/tutors/aboutme.mpl?userid=bucky><B>bucky(2189)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=bucky><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=52310\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Given:<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=A+=+A%5Bo%5D%2Ae%5E%28-0.18t%29 ALIGN=MIDDLE  ALT=\"A+=+A%5Bo%5D%2Ae%5E%28-0.18t%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "When t = 3 days, then you are told that A (the amount remaining) is 40 grams. Substitute<BR>\n" );
document.write( "these values into the equation to get:<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=40+=+A%5Bo%5D%2Ae%5E%28-0.18%2A3%29 ALIGN=MIDDLE  ALT=\"40+=+A%5Bo%5D%2Ae%5E%28-0.18%2A3%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "You need to solve this for <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=A%5Bo%5D ALIGN=MIDDLE  ALT=\"A%5Bo%5D\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "First multiply out the exponent:<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=40+=+A%5Bo%5D%2Ae%5E%28-0.54%29 ALIGN=MIDDLE  ALT=\"40+=+A%5Bo%5D%2Ae%5E%28-0.54%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "Finding <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=e%5E%28-0.54%29 ALIGN=MIDDLE  ALT=\"e%5E%28-0.54%29\"   DISABLED_style= \"max-width:90%; height:auto;\" > is just a calculator exercise. On most calculators the key will<BR>\n" );
document.write( "be marked <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=e%5Ex ALIGN=MIDDLE  ALT=\"e%5Ex\"   DISABLED_style= \"max-width:90%; height:auto;\" >. Enter -0.54 and press the key to get 0.582748252. Substitute that<BR>\n" );
document.write( "number into the equation to get:<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=40+=+A%5Bo%5D%2A%280.582748252%29 ALIGN=MIDDLE  ALT=\"40+=+A%5Bo%5D%2A%280.582748252%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "Now solve for <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=A%5Bo%5D ALIGN=MIDDLE  ALT=\"A%5Bo%5D\"   DISABLED_style= \"max-width:90%; height:auto;\" > by dividing both sides of this equation by 0.582748252 to get:<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=A%5Bo%5D+=+40%2F0.582748252+=+68.64027449 ALIGN=MIDDLE  ALT=\"A%5Bo%5D+=+40%2F0.582748252+=+68.64027449\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "So the answer is that you should start with 68.64027449 grams to have 40 grams left after<BR>\n" );
document.write( "three days.  Note that the closest answer in your list of answers is 68.6 grams.<BR>\n" );
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document.write( "Hope this work helps to get you familiar with solving exponential equations such as this.<BR>\n" );
document.write( "This type of equation crops up in chemistry, physics, electronics, math, and societal studies<BR>\n" );
document.write( "and you may need to understand how to handle them at some point. </SPAN>\n" );
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