9. The half-life of radium is 1690 years. If 30 grams are present now, how much will be present in 280 years? (Do not round until the final answer. Then round to the nearest tenth.) In (2) 1690 K A = Ao e 1690 1690k 2 = e In ( )=1690k Answers: K = ≈ 0.000410146 In (1) A = 30 @ 1690 - 280 ~26.7 grams

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How do I enter this into the calculator for either problem to arrive at the same answer?

**Transcription for Educational Website**

**Radioactive Decay and Half-Life Calculations**

(d) What is the half-life of strontium 90? (Round to the nearest tenth)

**Note:** The *half-life* is the time it takes an initial amount of a radioactive substance to decay to one half of it.

\[
\frac{1}{2}A_0 = A_0 e^{-0.0244t}
\]

\[
\frac{1}{2} = e^{-0.0244t}
\]

\[
\ln\left(\frac{1}{2}\right) = \ln\left(e^{-0.0244t}\right)
\]

\[
t = \frac{\ln\left(\frac{1}{2}\right)}{-0.0244} \approx 28.4 \text{ years}
\]

---

9. The half-life of radium is 1690 years. If 30 grams are present now, how much will be present in 280 years? (Do not round until the final answer. Then round to the nearest tenth.)

\[
\frac{1}{2}A_0 = A_0 e^{1690k}
\]

\[
\frac{1}{2} = e^{1690k}
\]

\[
\ln\left(\frac{1}{2}\right) = 1690k
\]

\[
k = \frac{\ln\left(\frac{1}{2}\right)}{1690} \approx -0.000410146
\]

\[
A = 30 \cdot e^{\left(\frac{\ln\left(\frac{1}{2}\right)}{1690} \cdot 280\right)} \approx 26.7 \text{ grams}
\]

---

**Answers:**

1. $451.00
2. 2.13 years
3. 3.94 years; 3.85 years
4. 9.576%
5. Bank B
6. $172.20
Transcribed Image Text:**Transcription for Educational Website** **Radioactive Decay and Half-Life Calculations** (d) What is the half-life of strontium 90? (Round to the nearest tenth) **Note:** The *half-life* is the time it takes an initial amount of a radioactive substance to decay to one half of it. \[ \frac{1}{2}A_0 = A_0 e^{-0.0244t} \] \[ \frac{1}{2} = e^{-0.0244t} \] \[ \ln\left(\frac{1}{2}\right) = \ln\left(e^{-0.0244t}\right) \] \[ t = \frac{\ln\left(\frac{1}{2}\right)}{-0.0244} \approx 28.4 \text{ years} \] --- 9. The half-life of radium is 1690 years. If 30 grams are present now, how much will be present in 280 years? (Do not round until the final answer. Then round to the nearest tenth.) \[ \frac{1}{2}A_0 = A_0 e^{1690k} \] \[ \frac{1}{2} = e^{1690k} \] \[ \ln\left(\frac{1}{2}\right) = 1690k \] \[ k = \frac{\ln\left(\frac{1}{2}\right)}{1690} \approx -0.000410146 \] \[ A = 30 \cdot e^{\left(\frac{\ln\left(\frac{1}{2}\right)}{1690} \cdot 280\right)} \approx 26.7 \text{ grams} \] --- **Answers:** 1. $451.00 2. 2.13 years 3. 3.94 years; 3.85 years 4. 9.576% 5. Bank B 6. $172.20
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