A radioactive substance decays according to the formula Q(t)=Q0eâkt where Q(t) denotes the amount of the substance present at time t (measured in years),
Q0 denotes the amount of the substance present initially, and k (a positive constant) is the decay constant.
(a) Find the half-life of the substance in terms of k.
(b) Suppose a radioactive substance decays according to the formula
Q(t)=15eâ0.0001438t
How long will it take for the substance to decay to half the original amount? (Round your answer to the nearest whole number.) yr