1. The problem statement, all variables and given/known data The number of radioactive nuclei in a particular sample decreases over a period of 26 days to one-fifteenth of the original number. What is the half-life of the radioactive material, in days? 2. Relevant equations R=DN/Dt=(lambda)(N)=(N)(ln2/T1/2) 3. The attempt at a solution DN= N - (1/15)N DT=26 days Plugged these in and solved for T(1/2), but CAPA says my answer is wrong.