If we start with 400 atoms of a radioactive substance, how many would remain after one half-life? After 2 half-lives? After 3 half-lives? After 4 half-lives?

how many would remain

after one half-life = 200 atoms

After 2 half-lives = 100 atoms

After 3 half-lives = 50 atoms

After 4 half-lives = 25 atoms

Explanation:

Given;

Initial amount = 400 atoms

Half life is the time taken to decay half of a radioactive material.

how many would remain after one half-life;

= 400/2 = 200 atoms

After 2 half-lives;

= 400/2^2 = 400/4

= 100 atoms

After 3 half-lives

= 400/2^3 = 400/8

= 50 atoms

After 4 half-lives

= 400/2^4 = 400/16

= 25 atoms