Answer:
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
