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FRM Part I · FRM Exam Part I · Binomial Trees

A stock is at 100. In each of two periods it moves up by a factor of 1.10 or down by a factor of 0.90. The per-period risk-free rate is 0%, so the risk-neutral up probability is 0.50. For a European call with strike 100 expiring after two periods, what is the delta at time 0?

The initial delta is 0.525. Roll back to the first-step nodes: the option is worth 10.5 after an up move and 0 after a down move. Dividing the 10.5 difference by the stock price difference of 20 gives 0.525.

  1. A0.525Correct
  2. B0.955
  3. C0.263
  4. D0.105

Explanation

Terminal prices are 121, 99 and 81, giving payoffs of 21, 0 and 0. The value at the up node (110) is 0.5 × 21 = 10.5, and at the down node (90) it is 0. Delta at time 0 = (10.5 - 0)/(110 - 90) = 0.525. The 0.955 option is the delta at the up node, 21/(121 - 99), which is a later-step delta.

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