Question

The half-life of Po-214 is 0.001 seconds. How much of a 10-gram sample is left after 0.003 seconds?

Answer 1

You would be left with 1.25 g.

After 0.001 second, 10 grams decays to 5 grams.

After another 0.001 second, 5 g decays to 2.5 g. (Total time 0.002 s; two half-lives have passed)

After another 0.001 second, 2.5 g decays to 1.25 g. (Total time 0.003 s; 3 half-lives have passed)