Half-lives are how long it takes for half of a substance to decay. If you start with a certain amount and it decays for a certain amount of half-lives, you are dividing by , where <em>x</em> is equal to the amount of half-lives.
In order to solve this question, simply divide the starting value by 2 raised to the value of half-lives.
Okay well I do it like this. 3+8=11. I put a 1 down and carry the other. so I do 7+0+1=8 so now I have 81, and last I do 6+3=9. so the answer would be 981.
