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FRM Part I · FRM Exam Part I · Binomial Trees

A stock is at 100 on a two-step binomial tree. Each step has u = 1.10 and d = 0.90, and the gross risk-free return per step is 1.02. What is the value of a European call with a strike of 100 expiring after two steps?

The call is worth about 7.27. The risk-neutral up probability is 0.60. Only the double-up node, at 121, gives a payoff of 21, with probability 0.36. The expected payoff of 7.56 is discounted over two periods at 1.02 per period, giving 7.27.

  1. A7.27Correct
  2. B7.41
  3. C5.05
  4. D12.11

Explanation

p = (1.02 - 0.90)/0.20 = 0.60. The terminal prices are 121, 99 and 81, so only the uu node pays off, with a payoff of 21. Its probability is 0.36, so the value is 0.36 × 21/1.02² = 7.56/1.0404 = 7.27. Discounting only once gives 7.41, which is wrong.

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