- 92

- 0

My answer: 11.7 mg. I came to this answer by recognizing that 24.6 yr is the duration of 2 half lives. Thus, 1/4 of the original amount will be present. Dividing 46.9 by 4 yields 11.725; however, I must use the correct number of significant figures (3, I believe), so my final answer is 11.7 mg.

Please tell me what I am doing wrong, because my answer has been marked wrong and I cannot figure out why.