document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=177442>Question 177442</A>: <I><SPAN STYLE=\"word-break: break-all;\"> My daughter missed this class friday and has a final monday morning..can you please show how to get answer and correct answer?  A 20g sample of a radioactive substance has a half life of 28 days.<BR>\n" );
document.write( "a.  how much of the sample is left after one year?<BR>\n" );
document.write( "b.  how many days will it take for the sample to reach 1 gram?\r<BR>\n" );
document.write( "\n" );
document.write( "Thank you for your help! </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #132484 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=132484\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> My daughter missed this class friday and has a final monday morning..can you please show how to get answer and correct answer? A 20g sample of a radioactive substance has a half life of 28 days.<BR>\n" );
document.write( "a. how much of the sample is left after one year?<BR>\n" );
document.write( "A(t) = Ao(1/2)^(t/n) where n is the half-life<BR>\n" );
document.write( "A(365) = 20(1/2)^(365/28)<BR>\n" );
document.write( "A(365) = 20(1/2)^(13.036)<BR>\n" );
document.write( "A(365) = 20*0.0001191<BR>\n" );
document.write( "A(365) = 0.00238 grams<BR>\n" );
document.write( "----------------------------<BR>\n" );
document.write( "Let me know if you cannot follow the logic of this solution.<BR>\n" );
document.write( "----------------------------------------------------------------\r<BR>\n" );
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document.write( "b. how many days will it take for the sample to reach 1 gram? <BR>\n" );
document.write( "1 = 20(1/2)^(t/28)<BR>\n" );
document.write( "1/20 = (1/2)^(t/28)<BR>\n" );
document.write( "Take the log of both sides to get:<BR>\n" );
document.write( "(t/28)log(1/2) = log(1/20)<BR>\n" );
document.write( "t/28 = log(1/20)/log(1/2)<BR>\n" );
document.write( "t/28 = 4.3219..<BR>\n" );
document.write( "t = 28*4.3219 = 121.013 days<BR>\n" );
document.write( "==================================<BR>\n" );
document.write( "Cheers,<BR>\n" );
document.write( "Stan H.<BR>\n" );
document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );