document.write( "Question 852103: The half-life of iodine-131 is 7.2 days. How long will it take for a sample of this substance to decay to 30% of its original amount? Round to one decimal place. \n" ); document.write( "

Algebra.Com's Answer #513129 by ewatrrr(24785) $\"\"$ $\"About$

You can put this solution on YOUR website!

 
\n" );
document.write( "Hi,
\n" );
document.write( "  0r   
\n" );
document.write( "Finding 'k' first
\n" );
document.write( " .5 = e^(-7.2k)
\n" );
document.write( " = k = .0963
\n" );
document.write( " .3 = e^(-.0963t)
\n" );
document.write( " = t
\n" );
document.write( "  \n" );
document.write( "

\n" );