document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1201597>Question 1201597</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Radioactive Carbon-14,which is found in all living things, has a half-life of 5700 years and can be used to date fossils. Suppose a fossil contains 15% of the amount of Carbon-14  that the organism contained when it was alive. Calculate the age of the fossil.  </SPAN>\n" );
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document.write( "Answer:  <font color=red size=4>15600 years old</font> (approximate)\r<BR>\n" );
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document.write( "a = starting amount = doesn't matter since it cancels out later<BR>\n" );
document.write( "0.15a = 15% of the starting amount\r<BR>\n" );
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document.write( "x = number of years<BR>\n" );
document.write( "y = amount of material remaining<BR>\n" );
document.write( "H = 5700 = half-life\r<BR>\n" );
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document.write( "Half-life formula<BR>\n" );
document.write( "y = a*(0.5)^(x/H)<BR>\n" );
document.write( "0.15a = a*(0.5)^(x/5700)<BR>\n" );
document.write( "0.15 = (0.5)^(x/5700)<BR>\n" );
document.write( "Log(0.15) = Log( (0.5)^(x/5700) )<BR>\n" );
document.write( "Log(0.15) = (x/5700)*Log(0.5)<BR>\n" );
document.write( "x/5700 = Log(0.15)/Log(0.5)<BR>\n" );
document.write( "x = 5700*Log(0.15)/Log(0.5)<BR>\n" );
document.write( "x = 15600.7038867473<BR>\n" );
document.write( "x = 15600\r<BR>\n" );
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document.write( "The substance is roughly 15600 years old.<BR>\n" );
document.write( "Round this however your teacher instructs.<BR>\n" );
document.write( "I decided to round to the nearest hundred.<BR>\n" );
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