# How much material will be left if a radioactive isotope has a half life of 1.3 billion years in 3.9 billion years?

##### 1 Answer

Jul 21, 2014

You will have 12.5 % of the parent material after 1.3 billion years.

This problem is like the one at

**Method 1**

In your problem, the number of half-lives is

The amount remaining after 3 half-lives is

100 % ×

**Method 2**