How much of radioactive actinium, in grams, will be left after 18 hours if the half-life is 6 hours and you start with 384 grams?

Answer 1

Because the half-life is 6 hours, the starting amount will be halved every 6 hours. Because there are 18 total hours, the starting amount will be divided by 2 (halved) three times. You will then have 1/6 of the starting amount, thus being 384 grams/ 6 = 48 grams.