Question

Bismuth-210 has a half-life of about 5 days.

After 15 days, how many milligrams of a 600 mg sample will remain?

Answer 1

so you know that after 5 days there is only 300 mg left (600/2) and then after another 5 days it would be in half again (150 mg) and so on. So find how many 5 days are in 15, and half 600 mg that many times.

15/5 = 3
600/2/2/2 = 75