1. The problem statement, all variables and given/known data The equilibrium concentration of C14/C12 ≈ 1.5×10−12 A 2.5 g sample of Carbon from an old tree fragment has an activity of 4.57 decays per minute. How old is the sample? 2. Relevant equations I'm pretty sure I use A(t)=λN(0)*exp(-tλ) but I am having trouble calculating N(0)! The amount of C14 c.f. C12 is so tiny I don't know how to manipulate the ratio to get the mass of C14, and thus the number of nucli, in the sample. Thanks!