3: Bismuth-210 has a half-life of about 5 days. After 15 days, how many milligrams of a 600 mg sample will remain? A O 75 mg B O150 mg C 200 mg D 475 mg

Radiologically, half lives describe the amount of time it takes for half the amount of the radioactive substance to decay. If you had 100g of a radioactive substance with a half life of one week, in seven days, only 50g would remain, and after another week, only 25g.

Fifteen days contains three half lives since the half life is 5 days long. Divide the starting amount by 2 for each half life that passes.

600g - 300g (1 HL) - 150g (2 HL) - 75g (3 HL)

So, only 75g of Bismuth-210 would remain after 15 days.

Only 75 g will still be there after 15 days.