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IAI Actuarial Core Principles · Economic Modelling · Binomial option-pricing model

Two investors disagree about the real-world probability that a share will rise in a one-period binomial model, one believing 0.7 and the other 0.4. Both accept the same share prices, up and down values and risk-free rate. Which statement about the no-arbitrage price of a call option on the share is correct?

The no-arbitrage price is identical for both investors. It is fixed by replication, equivalent to discounting expected payoff under the risk-neutral probability, which depends only on prices, up and down factors and the risk-free rate, not on beliefs or risk aversion.

  1. AThe investor with 0.7 should value it higher, since the up-move is more likely
  2. BThe price is the average of the two investors' expected payoffs
  3. CThe price is the same for both, as it depends only on the risk-neutral probabilityCorrect
  4. DThe price depends on each investor's risk aversion
  5. The price cannot be determined without the real-world probability

Explanation

The call can be replicated by shares and cash, so its arbitrage-free price depends only on the replicating portfolio cost, equal to the discounted expected payoff under q. Real-world probabilities and risk preferences do not enter.

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