What is the original mass of 12.5 mg after 3 half lives?

Answer 1

100 mg

= 50 mg after 1 hl

= 25 mg after 2 hl

= 12.5 mg after 3 hl

Answer 2

After 3 half-lives, the remaining mass is ( \frac{1}{8} ) of the original mass. So if the original mass is 12.5 mg, the final mass after 3 half-lives would be ( 12.5 , \text{mg} \times \frac{1}{8} = 1.56 , \text{mg} ).