Solution for QID #26798: How long will it take before twenty percent of our 1,000-gra | StudyHelpMe

How long will it take before twenty percent of our 1,000-gram sample of uranium-235 has decayed?  The decay equation is A(t)=A_0e^{Kt} , where t is the time for the decay, and K is the characteristic of the material. Suppose T is the time it takes for half of the unstable material in a sample of a radioactive substance to decay, called its half-life. Prove that K= \frac{ln0.5}{T} . What is T for the uranium-235?