Curium-243 has a half-life of 285 days. In a sample of 5.6 grams of curium-243. how many grams will remain after 12 days?
You can use the formula:
Where N is the amount of radioactive isotopes left to the time "t" (in this case t is measured in days). In this case measured in grams.
Insert the numbers to get:
As a side note, I'm pretty sure Cm-243 has a lot longer half-life than that :P