1. The problem statement, all variables and given/known data At present, the concentration of uranium 235 in naturally occurring uranium deposits is approximately 0.77%. What will the concentration be one billion years from now? 2. Relevant equations N(t) = No e^ -(ln(2)/half-life)t 3. The attempt at a solution i attempted this problem and got an answer of .69%.. What i did was put XNo= .77No e^ -(ln(2)/half-life)t .. that was the No can cancel out.. and then I just solved for X.. I feel like I am close but just making a slight mistake.