A sample of radioactive material starts with 80 grams. After 3 half-lives have passed, how much radioactive sample remains?

After 3 half lives 10 g of radio active material left.

Explanation:

Given data:

Total amount of radio active material = 80 g

Amount left after 3 half lives = ?

Solution:

At time zero = 80 g

At first half life = 80 g/2 = 40 g

At 2nd half life = 40 g/2 = 20 g

At 3rd half life = 20 g/2 = 10 g

Thus, after 3 half lives 10 g of radio active material left.