document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1190431>Question 1190431</A>: <I><SPAN STYLE=\"word-break: break-all;\"> The half-time of a radioactive substance is 9 years. If 40 grams of the substance exist initially, how much will remain after 23.5 years?<BR>\n" );
document.write( "a) 0.077 grams<BR>\n" );
document.write( "b) 244.30 grams<BR>\n" );
document.write( "c) 6.11 grams<BR>\n" );
document.write( "d) 2.49 grams<BR>\n" );
document.write( "e) 6.55 grams </SPAN>\n" );
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document.write( "Half-life formula<BR>\n" );
document.write( "y = a*(0.5)^(x/h)<BR>\n" );
document.write( "Alternatively, you can represent the 0.5 as 1/2\r<BR>\n" );
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document.write( "a = initial amount<BR>\n" );
document.write( "h = half-life, the amount of time it takes to cut in half<BR>\n" );
document.write( "x = number of years<BR>\n" );
document.write( "y = amount left over after x years pass by\r<BR>\n" );
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document.write( "We have the following<BR>\n" );
document.write( "a = 40 grams<BR>\n" );
document.write( "h = 9 years<BR>\n" );
document.write( "x = 23.5 years\r<BR>\n" );
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document.write( "So,<BR>\n" );
document.write( "y = a*(0.5)^(x/h)<BR>\n" );
document.write( "y = 40*(0.5)^(23.5/9)<BR>\n" );
document.write( "y = 6.54692287587487 approximately<BR>\n" );
document.write( "y = <font color=red>6.55 grams</font><BR>\n" );
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document.write( " </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );