Question 611874
A radioactive substance has a half-life of 60 years.
 There is an accident that exposes a town with the radioactive substance.
 The area will be safe after 95% of the substance has decayed. How many years will that take?
:
The radioactive decay formula A = Ao*2^(-t/h) where:
A = amt after t time (.05)
Ao = initial amt (1)
t = time of decay
h = half-life of substance (60)
:
1*2^(-t/60) =  .05
{{{-t/60}}}ln(2) = ln(.05)
{{{-t/60}}} = {{{ln(.05)/ln(2)}}}
{{{-t/60}}} = -4.322
t = -60 * -4.322
t = 259.3 yrs