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I try to solve this exercise:

a) Calclculate the price of a 3-month European put option on a non-dividend-paying stock with a strike price of 45 when the current stock price is 40, the risk-free interest rate is 5% per annum, and the volatility is 40% per annum.

b) What dierence does it make to the option price if a dividend of 1.50 is expected in 2 months?

While I can solve a) im not able to solve b). My solution for a) is: $T=\frac{1}{4}, K=45, S_0=40,r=0.05,\sigma=0.4$ leads to $$d_{+}=\frac{\ln\left( \frac{S_0}{K}\right)-(r+\frac{\sigma^2}{2})T}{\sigma \sqrt T}=-0.7514$$ and $$d_{-}=-0.9514.$$ Hence the put option price is given by $$P_0=-S_0N(-d_{+})+Ke^{-rT}N(-d_{-})=5.9042.$$

Can anybody explain how b) works?

Greetings

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One solution is to calculate the annual dividend yield implied by that. $Div_{yield}=\delta=1.5/40$ and then replace the $r$ on $d_+$ by $r-\delta$.

A cleaner way would be to compute it using a binomial tree.

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    $\begingroup$ And I use the exact same formula for $P_0$? I don't use $-S_0 e^{-\delta T}$ instead of $-S_0$? $\endgroup$
    – user154085
    Jul 10, 2015 at 14:27
  • $\begingroup$ Yes, you are right. $\endgroup$
    – phdstudent
    Jul 10, 2015 at 14:41
  • $\begingroup$ Sorry for asking, but with "Yes, you are right." you mean that I have to use $-S_0e^{-\delta T}$? $\endgroup$
    – user154085
    Jul 10, 2015 at 17:14
  • $\begingroup$ Yes you have to use $-S_0e^{-\delta T}$ $\endgroup$
    – phdstudent
    Jul 10, 2015 at 17:29

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