Time of decays approximately 2.853 days
Given
mass = 320mg iodine-131
No=320 mg
Nt=250 mg
t1/2 = 8 days
Required
t=time of decays
Solution
General formulas used in decay:
[tex]\large{\boxed{\bold{N_t=N_0(\dfrac{1}{2})^{t/t\frac{1}{2} }}}[/tex]
Input the value
[tex]\tt 250=320.\dfrac{1}{2}^{t/8}\\\\log\dfrac{25}{30}=t/8.log~0.5\rightarrow t=2.853~days[/tex]