Question 1088855
So if you started with {{{100g}}}, in 820 days you'd have {{{(0.72)(100g)=72 g}}}.
So then,
{{{72=100e^(k(820))}}}
{{{e^(820k)=0.72}}}
{{{820k=ln(0.72)}}}
{{{k=ln(0.72)/820}}}
{{{k=-4.006x10^(-3)}}}
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a) {{{50=100e^(kt)}}}
{{{e^(kt)=1/2}}}
{{{kt=ln(1/2)}}}
{{{t[1/2]=ln(1/2)/k}}}
{{{t[1/2]=ln(1/2)*(820/ln(0.72))}}}
{{{t[1/2]=1730}}}{{{days}}}
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b){{{63=100e^(kt)}}} 
{{{t= ln(0.63)*(820/ln(0.72)) }}}
{{{t=1153}}}{{{days}}}