Question 372366
strontium-89 has a half-life of 50.6 days.
 How long will it take for 20 grams of strontium-89 to decay to 8 grams?
:
The half life formula: A = Ao*2^(-t/h)
where
A = resulting amt after t time
Ao = initial amt
t = time
h = half-life of substance
:
20*2^(-t/50.6) = 8
:
2^(-t/50.6) = {{{8/20}}}
:
2^(-t/50.6) = .4
:
Using nat logs
{{{-t/50.6}}}ln(2) = ln(.4)
{{{-t/50.6}}} = {{{ln(.4)/ln(2)}}}
{{{-t/50.6}}} = -1.3219
t = -50.6 * -1.3219
t ~ 66.9 days