Question 975956
{{{y=a*e^(-bx)}}}


{{{ln(y)=ln(a)-bx}}}
{{{ln(y)-ln(a)=-bx}}}
{{{ln(a/y)=bx}}}
{{{b=(1/x)ln(a/y)}}}


VALUE OF b:
{{{(1/20)ln(65/17.55)}}}
{{{highlight(b=0.06547)}}}


FIND HALF-LIFE:
{{{ln(a/y)=bx}}}, from earlier step,
{{{x=(1/b)ln(a/y)}}}
{{{x=(1/0.06547)ln(1/(1/2))}}}
{{{highlight(x=(1/0.06547)ln(2))}}}
-----That will be the half-life.  You can finish computing it.