Iodine-125 has a half-life of about 60 days.

How many milligrams of a 500 mg sample will remain after 300 days?

1. 0.6 mg

2. 7.8125 mg

3. 15.625 mg

4. 31.25 mg

We know that Iodine - 125 has a half life of 60 days.

300 : 60 = 5. It means that it was halved 6 times.

Therefore: 500 mg * 0.5^5 =

= 500 mg * 0.5 * 0.5 * 0.5 * 0.5 * 0.5 =

= 500 mg * 0.03125 = 15.625 mg

Answer: 3. 15.625 mg.