1. The problem statement, all variables and given/known data A radioactive sample contains 2.25g of an isotope with a half-life of 3.8 days. How much of the isotope in grams will remain after 11.0 days? 2. Relevant equations 3. The attempt at a solution Hi! I've just started college this semester. I'm taking Introductory Chemistry. Right now we are doing nuclear chemistry. This problem is confusing, though, because I'm not sure if I can just divide the half-life like a normal number.. My professor doesn't teach. Literally. I tried doing this problem this way: It starts off with 2.25g. After 3.8 days (one half-life) it's 1.125g. After 7.6 days (two half lives) it's 0.5625g. But in another half-life, 11.4 days would have passed. More than 11. In 11.4 days it would be 0.28125g. Is this correct? How would I calculate this? My book doesn't tell me.. Is there a specific way? It only tells me that it's "beyond the scope of this book". Please help!