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FRM Part I · FRM Exam Part I · The Black-Scholes-Merton Model

A non-dividend-paying stock has μ = 9% and σ = 30% per annum. Over a 4-year horizon, what is the standard deviation of the continuously compounded return (ln(S_T/S_0)) under BSM assumptions?

The standard deviation is σ√T = 30% × √4 = 60%. Volatility scales with the square root of time, not linearly, because variance of the log return grows proportionally to the horizon under geometric Brownian motion.

  1. A30%
  2. B60%Correct
  3. C120%
  4. D7.5%

Explanation

The variance of ln(S_T/S_0) is σ²T = 0.09 × 4 = 0.36, so the standard deviation is 0.60 or 60%. Option A ignores the horizon. Option C multiplies σ by T instead of √T. Option D divides σ by T.

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