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Concentration changes over time

AP.Chem: TRA‑3 (EU), TRA‑3.C (LO), TRA‑3.C.1 (EK), TRA‑3.C.2 (EK), TRA‑3.C.3 (EK), TRA‑3.C.4 (EK), TRA‑3.C.5 (EK), TRA‑3.C.6 (EK)
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Problem

The radioisotope start superscript, 198, end superscript, A, u decays to start superscript, 198, end superscript, H, g with a half-life of 2, point, 69 days.
If a sample initially contains 9, point, 10, start text, m, g, end text of start superscript, 198, end superscript, A, u, what mass of start superscript, 198, end superscript, A, u remains after 3, point, 50 days?
Write your answer using three significant figures.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • an exact decimal, like 0, point, 75
  • a multiple of pi, like 12, space, start text, p, i, end text or 2, slash, 3, space, start text, p, i, end text
start text, m, g, end text, start superscript, 198, end superscript, A, u
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