Math Problem Statement

Stock X has a standard deviation of return of 30%. Stock Y has a standard deviation of return of 20%. The correlation coefficient between the two stocks is 0.33. If you invest 60% of your funds in Stock X and 40% in Stock Y.

The standard deviation of your portfolio is, therefore ______%.

(Please enter your answer as a percentage to two decimal places. i.e. 12.35 rather than 0.1235)

Solution

The formula for the standard deviation of a two-asset portfolio is given by:

σp=wX2σX2+wY2σY2+2wXwYσXσYρXY\sigma_p = \sqrt{w_X^2 \cdot \sigma_X^2 + w_Y^2 \cdot \sigma_Y^2 + 2 \cdot w_X \cdot w_Y \cdot \sigma_X \cdot \sigma_Y \cdot \rho_{XY}}

Where:

  • σp\sigma_p is the standard deviation of the portfolio,
  • wXw_X and wYw_Y are the weights of Stock X and Stock Y, respectively,
  • σX\sigma_X and σY\sigma_Y are the standard deviations of Stock X and Stock Y, respectively,
  • ρXY\rho_{XY} is the correlation coefficient between Stock X and Stock Y.

Given dataThe formula for the standard deviation of a two-asset portfolio is given by:

σp=wX2σX2+wY2σY2+2wXwYσXσYρXY\sigma_p = \sqrt{w_X^2 \cdot \sigma_X^2 + w_Y^2 \cdot \sigma_Y^2 + 2 \cdot w_X \cdot w_Y \cdot \sigma_X \cdot \sigma_Y \cdot \rho_{XY}}

Where:

  • σp\sigma_p is the standard deviation of the portfolio,
  • wXw_X and wYw_Y are the weights of Stock X and Stock Y, respectively,
  • σX\sigma_X and σY\sigma_Y are the standard deviations of Stock X and Stock Y, respectively,
  • ρXY\rho_{XY} is the correlation coefficient between Stock X and Stock Y.

Given

  • wX=0.60w_X = 0.60,
  • wY=0.40w_Y = 0.40,
  • σX=30%=0.30\sigma_X = 30\% = 0.30,
  • σY=20%=0.20\sigma_Y = 20\% = 0.20,
  • ρXY=0.33\rho_{XY} = 0.33.

Now, substituting the values into the formula:

σp=(0.60)2(0.30)2+(0.40)2(0.20)2+20.600.400.300.200.33\sigma_p = \sqrt{(0.60)^2 \cdot (0.30)^2 + (0.40)^2 \cdot (0.20)^2 + 2 \cdot 0.60 \cdot 0.40 \cdot 0.30 \cdot 0.20 \cdot 0.33}

Let's break it down step by step:

  1. (0.60)2(0.30)2=0.360.09=0.0324(0.60)^2 \cdot (0.30)^2 = 0.36 \cdot 0.09 = 0.0324,
  2. (0.40)2(0.20)2=0.160.04=0.0064(0.40)^2 \cdot (0.20)^2 = 0.16 \cdot 0.04 = 0.0064,
  3. 20.600.400.300.200.33=20.0720.33=0.047522 \cdot 0.60 \cdot 0.40 \cdot 0.30 \cdot 0.20 \cdot 0.33 = 2 \cdot 0.072 \cdot 0.33 = 0.04752.

Now, summing these:

σp2=0.0324+0.0064+0.04752=0.08632\sigma_p^2 = 0.0324 + 0.0064 + 0.04752 = 0.08632

Taking the square root:

σp=0.086320.2938\sigma_p = \sqrt{0.08632} \approx 0.2938

Converting this to a percentage:

σp29.38%\sigma_p \approx 29.38\%

Therefore, the standard deviation of your portfolio is 29.38%.

Would you like more details or have any questions?

Here are 5 related questions:

  1. How does the correlation coefficient between two stocks affect the portfolio's standard deviation?
  2. What would happen to the portfolio risk if the correlation coefficient was negative?
  3. How do you compute the expected return of a portfolio?
  4. Can you explain the significance of diversification in reducing portfolio risk?
  5. How would the portfolio's risk change if Stock X had a lower standard deviation?

Tip: Lower correlation between assets generally leads to better diversification and lower overall portfolio risk.

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Math Problem Analysis

Mathematical Concepts

Portfolio Theory
Statistics
Risk Management

Formulas

Portfolio standard deviation formula: σp = √(wX² * σX² + wY² * σY² + 2 * wX * wY * σX * σY * ρXY)

Theorems

Diversification Effect
Markowitz Portfolio Theory

Suitable Grade Level

Undergraduate Finance or Advanced High School (Grades 11-12)