Question

Krypton-91 is a radioactive substance that decays very quickly. The function Q(t)=Qoe^-kt models the radioactive decay of krypton-91. Q represents the quantity remaining after t seconds, and the decay constant, k, is approximately 0.07. How long will it take a quantity of krypton-91 to decay to 10% of its original amount? Round your answer to the nearest second.

Answer 1

Q(t) = 0.10Q
k = 0.07

plug and solve:

0.10Q = Q * e^-(0.07)t for t