If we start with 48 g of a radioactive substance with a 2 hour 12 life, how much is left after two half-lives? four half-lives?

Explanation:

 Half-life is the time taken for a radioactive material to decay to half its original composition:

   Original mass = 48g

   Half- life  = 2hr

 After four half lives;

           Initially:                48g

    First halving                24

    Second halving          12

    Third halving               6

    Fourth halving             3

After second half life, we would have 12g

At fourth halving, we would have 3g

ingenuity says that the answer is 2.7 m.