Question 978543
{{{y=p*e^(-kt)}}}


{{{ln(y)=ln(p)-kt}}}
{{{ln(y)-ln(p)=-kt}}}
{{{kt=ln(p)-ln(y)}}}
{{{k=(ln(p)-ln(y))/t}}}
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{{{k=(ln(4.75)-ln(12))/12}}}
{{{k=-0.07723}}}
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{{{y=p*e^(-0.07723*t)}}}


What you want to answer the question is this:
{{{highlight(t=(ln(p)-ln(y))/k)}}}, and let y=2, k already been found, and p given.