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FRM Part II · FRM Exam Part II · Portfolio Risk: Analytical Methods

A single-factor model gives a portfolio a beta of 0.9 to a market index with 20% annual volatility. The portfolio's residual (idiosyncratic) volatility is 8%, uncorrelated with the market. What is the portfolio's total annual volatility, to the nearest 0.1%?

Total volatility is about 19.7%. Systematic volatility is 0.9 times 20%, or 18%. Because residual risk is uncorrelated, variances add: 324 plus 64 equals 388, whose square root is 19.7%. Simply adding volatilities to get 26% would be wrong.

  1. A17.7%
  2. B19.7%Correct
  3. C26.0%
  4. D28.0%

Explanation

Systematic volatility = 0.9 x 20% = 18%. Total variance = 18%^2 + 8%^2 = 324 + 64 = 388 (in %^2), so volatility = sqrt(388) = 19.7%. Adding volatilities (26%) ignores that uncorrelated risks add in variance.

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