
Answer-first summary for fast verification
Answer: 24.0%
**Explanation:** To calculate the standard deviation of a two-asset portfolio, we use the formula: $$\sigma_p = \sqrt{w_A^2 \sigma_A^2 + w_B^2 \sigma_B^2 + 2w_A w_B \sigma_A \sigma_B \rho_{AB}}$$ Where: - $w_A = 0.30$ (weight of security A) - $w_B = 0.70$ (weight of security B) - $\sigma_A = 0.30$ (standard deviation of security A) - $\sigma_B = 0.25$ (standard deviation of security B) - $\rho_{AB} = 0.60$ (correlation between A and B) **Step-by-step calculation:** 1. Calculate $w_A^2 \sigma_A^2 = (0.30)^2 \times (0.30)^2 = 0.09 \times 0.09 = 0.0081$ 2. Calculate $w_B^2 \sigma_B^2 = (0.70)^2 \times (0.25)^2 = 0.49 \times 0.0625 = 0.030625$ 3. Calculate $2w_A w_B \sigma_A \sigma_B \rho_{AB} = 2 \times 0.30 \times 0.70 \times 0.30 \times 0.25 \times 0.60$ - First: $0.30 \times 0.70 = 0.21$ - Then: $0.30 \times 0.25 = 0.075$ - Then: $0.21 \times 0.075 = 0.01575$ - Then: $0.01575 \times 0.60 = 0.00945$ - Finally: $2 \times 0.00945 = 0.0189$ 4. Sum all components: $0.0081 + 0.030625 + 0.0189 = 0.057625$ 5. Take the square root: $\sqrt{0.057625} = 0.24005$ or **24.0%** **Verification:** - Option A (16.8%) is too low - this would be the result if the correlation was negative or if we used a simple weighted average without considering correlation. - Option C (26.5%) is too high - this would be closer to a simple weighted average of the standard deviations (0.30 × 30% + 0.70 × 25% = 26.5%), but this ignores the diversification benefit from less-than-perfect correlation. **Key Concept:** The portfolio standard deviation is less than the weighted average of individual standard deviations when correlation is less than 1.0, demonstrating the diversification benefit.
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A portfolio manager creates the following two-security portfolio:
| Security | Security Weight | Expected Standard Deviation |
|---|---|---|
| A | 30% | 30% |
| B | 70% | 25% |
If the correlation of returns between the two securities is 0.60, the expected standard deviation of the portfolio is closest to:
A
16.8%
B
24.0%
C
26.5%