If each half life of a C14 isotope is 5730 years, how many years does it take for an 80 g sample to decay to 10 g

Question

If each half life of a C14 isotope is 5730 years, how many years does it take for an 80 g sample to decay to 10 g

Answer 1

Take 80g and cut it in half for each 5730 years: 80 -> 40 ->20 -> 10. The sample reaches a mass of 10g in 3 half-lives = 17,190 years.