In the diagram, AB = 10 and AC = 210. What is the perimeter of ABC?
A. 10 units
B. 10 + 2/10 units
C. 20 units
D. 20 + 210 units

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

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