I recently have been trying to model 2 step nuclear decay. I said that X decays into Y with a rate constant k_{x}. And Y decays into Z with rate constant k_{x}. I then set up the differential equation dy/dt=k_{x}x-k_{y}Y. I then substituted in X=X_{0}e^{-kxt} for X in the differential equation. The result when I solve the equation however has the term (k_{y}-k_{x}) in the demominator of a fraction which makes no sense to me because because what if they are equal? And what if k_{x} is greater than k_{y}? There shouldnt be a negative amount of Y. Once i find a place to host my work as a picture I can post that. Anyways if anyone knows of a correct equation to model this or could confirm or reject my original differential equation it would be appreciated. Thanks.