1. The problem statement, all variables and given/known data A radioactive material decays by simultaneous emission of two particles with respective half lives 1620 and 810 years. The time, in years, after which one-fourth of the material remains is: 2. Relevant equations 3. The attempt at a solution I'm confused whether the half lives mentioned are of the original radioactive material itself, or of the the particles which are formed. In any case, I'm really not sure of how to deal with two particle emission. I've only ever done single decays and basic half life calculations. Please help?