Answer :
Start with general exponential decay function:
P = e^{-kt}
Plug in given point (4,0.6) solve for k
k = ln 0.6/-4 to determine half-life,
set P = 0.5 , solve for t
t = 4* \n 0.5/ln 0.6
P = e^{-kt}
Plug in given point (4,0.6) solve for k
k = ln 0.6/-4 to determine half-life,
set P = 0.5 , solve for t
t = 4* \n 0.5/ln 0.6