How long will it take for 52.0% of a 0.00870 mg sample of radioactive iodine-131 to decay?

Question

The half-life of iodine-131 is 8.10 days, so give your answer in days.

Answer 1

0.48 = 0.5^(t/8.1)
t/8.1 = log(0.48)/log(0.5)
t = 8.1log(0.48)/log(0.5)
t = 8.577 days