Practice Problem 7
Calculate the fraction of 14C that remains in a sample after eight half-lives.
Half of the 14C present initially decays during the first half-life, half of what is left decays during the second half-life, and so on. The 14C left after eight half-lives is equal to one-half raised to the eighth power:
(1/2)8 = 0.00391
Less than 0.4% of the original is left after eight half-lives.