document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=691570>Question 691570</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The mass m(t) remaining after t days from a 25-g sample of thorium-234 is given by <BR>\n" );
document.write( "m(t)=25e^(-0.0277)t\r<BR>\n" );
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document.write( "a) How much of the sample will remain after 70 days? Round the answer to the nearest integer. (Answer should be in terms of grams)\r<BR>\n" );
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document.write( "b) After how long will only 10g of the sample remain? Round the answer to the nearest integer. (Answer should be in terms of days)\r<BR>\n" );
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document.write( "c) Find the half-life of thorium-234. Round the answer to the nearest integer. (Answer should be in terms of days)<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 #426768 by </B><A HREF=/tutors/aboutme.mpl?userid=stanbon><B>stanbon(75887)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=stanbon><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=426768\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> The mass m(t) remaining after t days from a 25-g sample of thorium-234 is given by <BR>\n" );
document.write( "m(t)=25e^(-0.0277)t <BR>\n" );
document.write( "a) How much of the sample will remain after 70 days? Round the answer to the nearest integer. (Answer should be in terms of grams)<BR>\n" );
document.write( "m(70) = 25*e^(-0.0277*70) = 3.5962 grams<BR>\n" );
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document.write( "b) After how long will only 10g of the sample remain? Round the answer to the nearest integer. (Answer should be in terms of days)<BR>\n" );
document.write( "25*e^(-0.0277t) = 10<BR>\n" );
document.write( "e^(-0.0277t) = 2/5<BR>\n" );
document.write( "-0.0277t = ln(0.4)<BR>\n" );
document.write( "t = 33.079 days<BR>\n" );
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document.write( "c) Find the half-life of thorium-234. Round the answer to the nearest integer. (Answer should be in terms of days)<BR>\n" );
document.write( "e^(-0.0277t) = 1/2<BR>\n" );
document.write( "-0.0277t = ln(.5)<BR>\n" );
document.write( "t = 25 days when rounded down<BR>\n" );
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document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( " </SPAN>\n" );
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