1. The problem statement, all variables and given/known data I learnt that radio-decay is exponential; say if A decays to B with constant y1 and B decays to C with constant y2 and C is stable, N1 is nuclei in A while N2 is nuclei in B. N1 = N0e-y1(t) 2. Relevant equations Then, I tried writing the decay equation for B, and hit a wall because N2 is no longer N0, as the amount originally is zero. 3. The attempt at a solution Then i tried to derive it: Amount = (decayed nuclei from A) + (decay of itself) N2 = INT A1 dt + INT A2 dt and I arrive with this crazy integration which I do not know how to solve. Are there any better ways to derive it?