Question

a 32 gram radioactive sample has a half-life of 2 days how much of the original sample remains after 6 days

Answer 1

First, we will get the "n", the number of half lives, it is the elapsed time over the half life. In the problem, the time is measured in days, so we have 

6/2 = 3 

to get the ending amount of radioactive sample, we have

32g x (1/2)³ = 4 grams of radioactive sample ⇒ the amount left after 6 days