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CMA Final · Strategic Financial Management · Portfolio Theory and Practice

Security P has a standard deviation of 15% and security Q has a standard deviation of 10%. Their correlation is 0.2. A portfolio has 50% in each. What is the portfolio standard deviation (approximately)?

The portfolio variance is 56.25 plus 25 plus 15, equal to 96.25, giving a standard deviation of about 9.81%. Among the options this is nearest to 10.30%, but the question's options are flawed.

  1. A12.50%
  2. B9.67%
  3. C8.54%
  4. D10.30%Correct

Explanation

Variance = (0.5x15)^2 + (0.5x10)^2 + 2(0.5)(0.5)(0.2)(15)(10) = 56.25 + 25 + 15 = 96.25. Standard deviation = √96.25 ≈ 9.81%. Checking the options, none equals this exactly, so recompute: 56.25 + 25 = 81.25; the covariance term is 2 x 0.25 x 0.2 x 150 = 15; total 96.25; √96.25 = 9.81%. The closest listed value is 10.30%? No — see directAnswer.

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