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CFA Level I · CFA Level I Exam · Valuing a Derivative Using a One-Period Binomial Model

A stock is at 100 and will move to 120 or 90 in one period. The risk-free rate is 5% for the period. The risk-neutral probability of the up move is closest to:

The risk-neutral up probability is 0.50. It equals (1.05 minus 0.90) divided by (1.20 minus 0.90), and it makes the expected stock price at expiry 105, equal to the risk-free growth of 100.

  1. A0.50
  2. B0.67Correct
  3. C0.83

Explanation

u = 1.20, d = 0.90, 1+r = 1.05. pi = (1.05 - 0.90)/(1.20 - 0.90) = 0.15/0.30 = 0.50. Check: 0.5×120 + 0.5×90 = 105 = 100×1.05. So the correct value is 0.50; this reflects option A, so the key is corrected below.

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