Question

Ac-225 has a half-life of 10 days. A sample has been on a shelf for a month. About how much of the sample is still radioactive?

Answer 1

1/8th of the original amount

Step-by-step explanation:

One month (30 days) is 3 half lives

so 1/2 * 1/2 * 1/2 = 1/8 th is left radioactive