Question

The half life of a radioactive isotope is 4 years. Starting with 5 gram of a sample of this isotope, how much would remain after 10 years?

Answer 1

Since the isotope has gone through `2.5` half-lives, it would only have `0.88g` left.

Explanation:

Well, if `n` is the number of half-lives elapsed, then there would be `100/2^n%` of the object left.

Since the isotope's half-life is `4` years, then after `10` years, it would have gone through `10/4=2.5` half-lives.

Plugging in `n=2.5`, there would be

`100/2^2.5%~~17.68%` of the original isotope left.

So, there would be `17.68%*5~~0.884g~~0.88g` of the isotope left.

Source:

https://en.wikipedia.org/wiki/Half-life