Suppose that the half-life of an element is 1000 years. how many half-lives will it take before one-eighth of the original sample remains? 8 125 12.5 3

3

Explanation:

The half-life of a radioactive isotope is the time it takes for the mass of the sample to halve.

This can be rewritten as follows:

where

m(t) is the mass of the sample at time t

m0 is the original mass of the sample

n is the number of half-lives that passed

We see that if we take n=3, the amount of original sample left is

So 3 (3 half-lives) is the correct answer.