I-123 is a radioisotope used to diagnose the function of the thyroid gland.?

It’s has a half life of 13.3 hours. What fraction of the diagnostic does of I-123 would be present in a patient 79.8 hours after it was administered?
1: 1/64
2: 1/8
3: 1/32
4: 1/16
1 answer 1