How many milligrams of an initial 63 of calcium-47 remain after 27 days?

To determine how much calcium-47 remains after 27 days, we need to consider its half-life, which is approximately 4.54 days. After 27 days, which is about six half-lives (27 days / 4.54 days ≈ 5.95), the remaining amount can be calculated using the formula ( \text{Remaining amount} = \text{Initial amount} \times \left( \frac{1}{2} \right)^{\text{number of half-lives}} ). Therefore, ( 63 , \text{mg} \times \left( \frac{1}{2} \right)^6 \approx 63 , \text{mg} \times 0.015625 \approx 0.984375 , \text{mg} ). Thus, approximately 0.98 mg of calcium-47 remains after 27 days.