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(a) Make use of an arbitrage argument to derive the put-call parity formula C+Ke

ID: 2788153 • Letter: #

Question

(a) Make use of an arbitrage argument to derive the put-call parity formula C+Ker(Tt) = P+X(t), relating the time t prices of a European call option C and a European put option P, both with the same expiry date T and the same strike price K, on an underlying asset whose current price is X(t). The risk-free interest rate is r. (a) Make use of an arbitrage argument to derive the put-call parity formula C+Ker(Tt) = P+X(t), relating the time t prices of a European call option C and a European put option P, both with the same expiry date T and the same strike price K, on an underlying asset whose current price is X(t). The risk-free interest rate is r. (a) Make use of an arbitrage argument to derive the put-call parity formula C+Ker(Tt) = P+X(t), relating the time t prices of a European call option C and a European put option P, both with the same expiry date T and the same strike price K, on an underlying asset whose current price is X(t). The risk-free interest rate is r.

Explanation / Answer

                              Outcome at T

Protective put         Put expire in Money                  Call expire in money

                              

Asset                            Xt                                                                          Xt

Long Put                      K- Xt                                                                    0

Total                               K                                                     Xt

Fiduciary call

Long call                         0                                                   Xt-K

Risk free bond               K                                                      K

Total                               K                                                      Xt

When put in the money protective put=Fiduciary call=K

When Call in the money protective put=Fiduciary call=XT

If protective put not equal to fiduciary call arbitrager will create synthetic position and use arbitrage technique that is buy cheap sell high to bring price back where Protective put=fiduciary call