Chemistry
posted by Anonymous .
The halflife of phosphorus32 is 14.26 days. The decay constant is k=4.86×10−2/days. If you accidentally spill phosphorus32 onto your shoe, how long would it take before 99.9% of the radioactive material has decayed so that you can safely wear the shoes again?

.001=e^.692t/th
.693*t/14.26 = ln .001
t= 142 days? check that. 
ln(No/N) = kt
Substitute for No = 100
N = 10099.9
Solve for t in days. 
Yeah, thanks.