You have 2000 g of radioactive substance with a half-life of 100 years four half-lives go by how many grams do you have the radioactive substance do you have left

after 4 half-lives, 125g is left

Explanation:

The half-life of a radioactive substance is the time it takes for the substance to decay by half its original mass.

In this example, we are asked to find the remaining mass after four half-lives.

What we will simply do is to reduce the starting mass by half, after each half-life decay. this is done as follows:

1st half-life decay: starting mass 2000g

final mass = 2000g ÷ 2 = 1000g

2nd half-life decay: starting mass = 1000g

final mass = 1000 ÷ 2 = 500

3rd half-life decay: starting mass = 500

final mass = 500 ÷ 2 = 250g

4th half-life decay: starting mass = 250g

final mass = 250 ÷ 2 = 125g

∴ after 4 half lives, 125g is left