The half-life of bismuth is 5 days. How much of a 100 gram sample will remain after 20 days?

a. 50 grams

b. 12.5 grams

c. 6.25 grams

d. 0 grams

Half-life is the duration needed for a compound to decay into half of its initial weight. In this case, the initial weight is 100gram. The calculation for the final weight should be:

final weight = initial weight * (1/2) ^ (duration/half-life)

final weight = 100 grams * (1/2) ^ (20days/5 days)

final weight = 100 grams * (1/2) ^ (4)

final weight = 100 * 1/16 = 100/16 gram = 6.25 grams