Ytterbium decays 50% every 4.2 days. How much of an 80g sample would be left after 54.6 days?

0.00116875 mg = 1.16875 micrograms

50 % decay 42 days = 10 x 4.2days = 0.0935mg = 93.5mcg

50% 12.6 days = 3 x 4.2 days = 0.0116875 mg = 1.16875mcg.

We check

Day group 1 = 40gm

Day group 2 = 20gm

Day group 3 = 10gm

Day group 4 = 5gm

Day group 5 = 2.5 gm

Day group 6 = 1.25gm

Day group 7 = 0.75mg

Day group 8 = 0.375mg

Day group 9 = 0.187mg

Day group 10 = 0.0935mcg

Day group 11 = 0.04675mcg

Day group 12 = 0.023375mcg

Day group 13 = 0.0116875mcg