Course MFE/3F Practice Exam 4 Solutions

Transcription

1 Course MFE/3F Practice Exam 4 Solutions The chapter references below refer to the chapters of the ActuarialBrew.com Study Manual. Solution D Chapter, Prepaid Forward Price of $ We don t need the information provided in statement (i) to answer this question. The usual formula for a prepaid forward price is: P -d T F0, T ( S) = S(0) e Let s find the prepaid forward price of $, in euros. From the perspective of a eurodenominated investor, the initial asset price is: = x(0).30 From the perspective of a euro-denominated investor, the dividend yield of $ is 6%. The prepaid forward price of one dollar, in euros, is therefore: e = e = x(0).30 The prepaid forward price of $,000, in euros, is: ,000 = Solution B Chapter 5, Itô s Lemma We have: () Gt () = e Zt The partial derivatives are: Z Z GZ = e GZZ = e Gt = 0 This results in: Zt ( ) Zt ( ) dg() t GZdZ GZZ( dz) Gtdt e dz() t () e dz() t 0dt Zt () Zt () e dz( t) e dz( t) Zt () Zt () e dz( t) e dt (because [ dz( t)] dt) GtdZt () () 0.5 Gtdt () 0.5 Gtdt ( ) GtdZt ( ) ( ) ActuarialBrew.com 04 Page

2 Dividing both sides by Gt ( ) results in: dg() t Gt () = 0.5 dt + dz( t) Solution 3 D Chapters 3 and 4, Greeks in the Cox-Ross-Rubinstein Model The values of u and d are: s h 0.30 u = e = e = s h d = e = e = The risk-neutral probability of an upward movement is: ( r-d ) h ( )() e -d e p* = = = u-d The stock price tree and its corresponding tree of option prices are: Stock American Put If the stock price initially moves down, then the resulting put price is $ This price is in bold type above to indicate that it is optimal to exercise early at this node: = The exercise value of is greater than the value of holding the option, which is: e -0.09() (0.4957) ( )(4.5594) =.900 [ ] The current value of the American option is: [ ] e -0.09() (0.4957)(0.975) + ( )(4.959) = ActuarialBrew.com 04 Page

3 In the CRR model, the stock price after one up movement and one down movement is equal to the initial stock price. Therefore, the formula for theta can be simplified: ( Sud - S) Vud -V -( Sud -S) D( S,0) - G( S,0) q ( S,0) = h (50-50) Vud -V -(50-50) D( S,0) - G( S,0) = h Vud - V = h The value of theta is: Vud - V q ( S,0) = = = h Solution 4 A Chapter 9, Delta-Gamma Hedging The gamma of the position to be hedged immediately after the sale of the call options is the quantity of the call options held times the gamma of each call option: = We can solve for the quantity, Q, of the put option that must be purchased to bring the hedged portfolio s gamma to zero: Q = 0.00 Q = The delta of the position becomes: (- 0.8) = The quantity of underlying stock that must be purchased, of the position being hedged: Q S = Q S, is the opposite of the delta Therefore, in order to delta-hedge and gamma-hedge the position, we must buy 85. units of stock and purchase 48.6 units of the put option. Solution 5 D Chapter 3, Replication The end-of-year payoffs of the call and put options in each scenario are shown in the table below. The rightmost column is the payoff resulting from buying the put option and selling the call option. ActuarialBrew.com 04 Page 3

4 Scenario End of Year Price of Stock A End of Year Price of Stock B P A (5) Payoff C B (50) Payoff PA(5) - C B(50) Payoff $300 $ $00 $ $50 $ We need to determine the cost of replicating the payoffs in the rightmost column above. We can replicate those payoffs by determining the proper amount of Stock A, Stock B, and the risk-free asset to purchase. Let s define the following variables: A = Number of shares of Stock A to purchase B = Number of shares of Stock B to purchase C = Amount to lend at the risk-free rate Since Stock A pays a $0 dividend at time 0.5, each share of Stock A that is purchased provides its holder with the final price of Stock A at time plus the accumulated value of $0. Since Stock B pays continuously compounded dividends of 8%, each share of stock B 0.08 purchased at time 0 grows to e shares of Stock B at time. We have 3 equations and 3 unknown variables: Scenario : È 0.(0.5) e A + 0B + Ce = 0 Î Scenario : È 0.(0.5) e A + 0B + Ce = 5 Î Scenario 3: È 0.(0.5) e A + 50e B + Ce = -5 Î Subtracting the first equation from the second equation allows us to solve for A: È 0.(0.5) + - È 0.(0.5) 00 0e A e A = 5 Î Î 5 A = = - 0.(0.5) 0.(0.5) e e 8 The equation associated with Scenario can now be used to find C: 0.(0.5) e A 0B Ce 0 0.(0.5) 0. 0.(0.5) 0. C 300 0e Ae 300 0e e ActuarialBrew.com 04 Page 4

5 We use the equation associated with Scenario 3 to find B: È 0.(0.5) e A + 50e B + Ce = -5 Î - È 0.(0.5) e + 50e B e = -5 Î 8 B = The cost now of replicating the payoffs resulting from buying the put and selling the call is equal to the cost of establishing a position consisting of A shares of Stock A, B shares of Stock B, and C lent at the risk-free rate. Since the price of Stock A is $00 and the price of Stock B is $50, we have: - 00A + 50B + C = ( ) = Solution 6 B Chapter 8, Black-Derman-Toy Model In each column of rates, each rate is greater than the rate below it by a factor of: i h e s Therefore, the missing rate in the third column is: -s e i = = The missing rate in the fourth column is: -s e i = = We do not need to calculate the missing rate in the fourth column because the value of a year-3 caplet does not depend on the interest rate in the fourth year, but we included it here for completeness. The tree of short-term rates is: 43.53% 6.65% 0.77% 30.7% 5.00% 9.77% 7.35%.68% 4.67% 5.30% ActuarialBrew.com 04 Page 5

6 The caplet pays off only if the interest rate at the end of the second year is greater than 6.00%. The payoff table is: N/A N/A N/A N/A The payments have been converted to their equivalents payable at the end of years. The calculations are shown below: 00 ( ) = ( ) = The present value of these payments is the value of the 3-year caplet: È T - * V0 = E ÍVT Í ( + r ) Î i = 0 i = =.66 (.5)(.077) (.5)(.077) (.5)(.735) Solution 7 C Chapter, Chooser Options The price of the chooser option can be expressed in terms of a put option and call option: -d ( ) ( T -t 0 ( ) ) - 0 ( r-d )( T -t Eur ) Price of Chooser Option = P S, K, T + e C S, Ke, t Eur The risk-free interest rate and the dividend yield are equal, so the put option has the same strike price as the call option: -0.08(4-) -( )(4-) ( ) Eur ( ) Price of Chooser Option = PEur 00,95,4 + e C 00,95 e, -0.08() Price of Chooser Option = PEur (00,95,4) + e CEur(00,95,) We can use put-call parity to find the value of the -year call option: 0.08() 0.08() CEur (00,95,) Ke e S0 PEur (00,95,) 0.08() 0.08() CEur (00,95,) 95e 00e.93 CEur (00,95,) ActuarialBrew.com 04 Page 6

7 We can now solve for the price of the 4-year put option: 0.08() Price of Chooser Option PEur(00,95,4) e CEur (00,95,) 0.08() 8.73 PEur(00,95,4) 6.907e PEur(00,95,4) Solution 8 A Chapter 8, Elasticity The values of d and d are: We have: ln( S/ K) + ( r - d s ) T ln(75 / 80) + ( ) 0.75 d = = s T = d = d - s T = = N( d ) N ( ) N( d ) N (0.48) The value of the European put option is: rt T PEur Ke N( d) Se N( d) 0.085(0.75) 0.04(0.75) 80e e The delta of the put option is: T 0.04(0.75) Put e N( d ) e The elasticity of the put option is: S 75 ( ) V Solution 9 A Chapter 5, Itô s Lemma The expression for Gt ( ) is: G S = t ActuarialBrew.com 04 Page 7

8 The partial derivatives are: t - GS = ts t - GSS = t( t -) S t Gt = S ln S From Itô s Lemma and the multiplication rules, we have: dg() t = GSdS() t + GSS[ ds()] t + Gtdt t- t- t = ts ds() t + 0.5( t t - ) S [ ds()] t + S lnsdt [ ] t- t- t = ts.5sdt SdZ 0.5 t( t ) S S dt S lnsdt t t t t =.5tS dt + ts dz t( t - ) S dt + S ln Sdt Since t G S, let s divide both sides by t S and reorganize the expression: dg() t =.5tdt + tdz t( t - ) dt + lnsdt Gt () =.5tdt + 0.5t dt - 0.5tdt + ln Sdt + tdz ( 0.5 ln ) = t + t + S dt + tdz We can find an expression for the natural log of S: t G = S lng = tln S lng ln S = t Substituting this in for the natural log of S, we have: dg() t Ê ln G() t ˆ = Á0.5t + t + dt + tdz Gt () Ë t Solution 0 B Chapter, Put-Call Parity From put-call parity: C ( K, T) + Ke = S + P ( K, T) Eur -rt Ke = S + P ( K, T )-C ( K, T ) -3r -3r 0 90e = e = r = ln(0.879) r = rt Eur 0 Eur Eur ActuarialBrew.com 04 Page 8

9 The continuously compounded risk-free interest rate is 4.30%. Solution D Chapter, Propositions Dewey is correct, because the prices of the 70-strike and 75-strike puts violate Proposition. According to Proposition, if the following is violated, then arbitrage is available: rt PEur ( K) - PEur ( K) ( K - K) e - Proposition is violated since: P (75) P (70) ( ) e Eur Eur ( ) e Since Proposition is violated, arbitrage can be obtained by entering into a put bull spread consisting of buying the 70-strike put and selling the 75-strike put. This results in a positive cash flow at time 0 of: P(75) - P(70) = 4.75 The positive cash flow can be lent at the risk-free rate, resulting in a positive, time cash flow of: e = Any negative cash flows produced by the put bull spread will be more than offset by the $ The payoffs of the put bull spread are graphed below: Payoff Put Bull Spread Payoff S T 5 Since $ is greater than even the worst case result from the put bull spread, Dewey is correct, and his strategy produces arbitrage profits. Louie is also correct, because the call prices violate Proposition 3. According to Proposition 3, if the following is violated, then arbitrage profits are available: CK ( ) - CK ( ) CK ( ) - CK ( 3) K - K K3 - K ActuarialBrew.com 04 Page 9

10 Proposition 3 is violated, since: C(60) -C(70) C(70) -C(75) < < < 0.4 Since Proposition 3 is violated, arbitrage can be obtained by entering into an asymmetric butterfly spread, where l 60-strike call options are purchased for each 70-strike call option sold and: K3 - K l = = = K3 - K Arbitrage is earned if we create an asymmetric butterfly spread by purchasing 3 of a 60- strike call option, selling 70-strike call option, and purchasing 3 of a 75-strike call option. We can scale this up by multiplying by 6, giving us the strategy outlined in the question: purchase of the 60-strike calls, sell 6 of the 70-strike calls, and purchase 4 of the 75-strike calls. This results in a positive cash flow at time 0 of: = 4.00 An asymmetric butterfly spread produces only non-negative payoffs. The payoffs of the asymmetric butterfly spread are graphed below: Payoff 0 Asymmetric Butterfly Spread Payoff S T Since Louie is being paid to enter into an asymmetric butterfly spread, his strategy produces arbitrage profits. Solution D Chapter, Factors Affecting Premiums Statement I is false, because if the time to maturity is increased so that it occurs after a liquidating dividend are paid, then the European call option expires worthless. (See page 80 of the third edition of the Derivatives Markets textbook.) ActuarialBrew.com 04 Page 0

11 Statement II is true, because before expiration an American call option on a non-dividend paying stock can be sold for more than its exercise value. (See page 77 of the third edition of the Derivatives Markets textbook.) Statement III is true because an American option can always be turned into a shorterlived American option. (See page 76 of the third edition of the Derivatives Markets textbook.) Solution 3 A Chapter 6, Black-Scholes Equation We can use the Black-Scholes equation to find rv : SS S t 0.5 s S V + ( r - d) SV + V = rv 0.5(0.30) (5) (0.45) + ( )(5)(0.64) = rv = rv The expected change per unit of time under the risk-neutral distribution is the risk-free rate times the value of the option: * E [ dv] = rv = dt Alternative Solution The stock process under the risk-neutral probability measure is: ds() t = ( r - d) S() t dt + ss() t dz () t dst () = ( ) Stdt () StdZt () () ds( t) = 0.06 S( t) dt S( t) dz ( t) Using Itô's Lemma and using the multiplication rules to simplify, we have: [ ] S SS t dv () t = V ds() t V ds() t + V dt = V 0.06 ( ) 0.30 ( ) ( ) ( ) 0.30 ( ) S È Stdt StdZt VSS È Stdt StdZt ( ) Î + + Î + + Vdt t = 0.06 VSS( t) dt VSS( t) dz( t) + 0.5VSS 0.09[ S( t)] dt + Vtdt = 0.06 V S( t) V [ S( t)] + V dt V StdZt () () ( ) S SS t S The expected value of dv ( t ) under the risk-neutral probability measure is: [ ] È ÍÎ( ) ( S SS t) * * E dv( t) = E 0.06 V ( ) [ ( )] 0.30 ( ) SS t + VSS S t + Vt dt + VSS t dz( t) * = 0.06 V S( t) V [ S( t)] + V dt because E ÈdZ ( t) Î = 0 ActuarialBrew.com 04 Page

12 Using the values at time t = 3, we have: E * [ dv(3) ] dt = 0.06 VSS(3) VSS[ S(3)] + Vt = = Solution 4 D Chapter 4, Multiplication Rules To keep the presentation from becoming too cluttered, we drop the functional relationships and conditional statement from the notation until the end. We have: dx( t) = 0.05Xdt XdZ dq( t) = 0.3Qdt + 0.0QdZ We begin by multiplying the expression out: EÎ ÈdX() t dq() t X(), t Q() t = E Xdt + XdZ Qdt + QdZ = E Xdt Qdt + X QdtdZ + Xdt QdZ + X QdZdZ [( ) ( )] [ 0.05 (0.3) 0.40 (0.3) 0.05 (0.0) 0.40 (0.0) ] The first 3 terms in the expression become zero because of the following multiplication rules: ( dt) = 0 dt dz = 0 For the fourth term, we make use of the following multiplication rule: dz dz = dt After applying the multiplication rules, we have: E (0.0) dzdzxq E (0.0)( dt) XQ 0.08XQdt Including the functional relationships, this is written as: 0.08 X( tqtdt ) ( ) ActuarialBrew.com 04 Page

13 Solution 5 E Chapter 7, Black-Scholes Formula for Currencies Brad wants to give up $6,500 and receive 50,000 at the end of 6 months. This can be accomplished with either of different purchases: 50,000 dollar-denominated call options on euros, each with a strike price of $.5. 6,500 euro-denominated put options on dollars, each with a strike price of Therefore, the correct answer must be either Choice B or Choice E. Let s find the price of the dollar-denominated call options. The values of d and d are: We have: ln( x0 / K) ( r rf 0.5 ) T ln(.5 /.5) ( )(0.5) d T d d T Nd ( ) N (0.90) Nd ( ) N (0.3435) The value of the call option is: rt f rt CEur x0e N( d) Ke N( d) 0.04(0.5) 0.07(0.5).5e e The value of 50,000 of the dollar-denominated call options is: $ ,000 $, Therefore, Choice B is not correct. The 50,000 dollar-denominated calls with a strike price of $.5 (described in Choice B) allow their owner the right to give up $6,500 to obtain 50,000. Likewise, 6,500 eurodenominated puts with a strike price of 0.80 (described in Choice E) allow their owner the right to give up $6,500 to obtain 50,000. Since both option positions have the same payoff, they must have the same current cost: $, =, $.5 / Therefore, Choice E is correct. ActuarialBrew.com 04 Page 3

14 Alternatively, we can use a relationship from Chapter of the ActuarialBrew.com Study Manual to find the cost of one of the euro-denominated put options: Ê ˆ C $ (x t,k,t - t) = xtkp Á,,T - t Ë x t K =.5.5 P 0.80,0.80,0.5 P ( 0.80,0.80,0.5) = ( ) The value of 6,500 of the put options is therefore: 6, =, Solution 6 A Chapter 7, Options on Currencies Since the call option is euro-denominated, we use the euro as the base currency. This means that the current exchange rate is: x 0 = 35 We also have: r = 0.05 r = 0.05 f The values of d and d are: We have: /35 ln ( ) 0.5 ln( x0 / K) ( r rf 0.5 ) T d T d d T Nd ( ) N (.867) Nd ( ) N (.05867) The value of the call option is: rt f rt CEur x0e N( d) Ke N( d) 0.05(0.5) 0.05(0.5) e e Since the call option is denominated in euros, the price of the call option is euros. ActuarialBrew.com 04 Page 4

15 Solution 7 C Chapter 3, Estimating Parameters of the Lognormal Distribution The quickest way to do this problem is to input the data into a calculator. Using the TI-30XS MultiView, the procedure is: [data] [data] 4 (enter the data below) (to clear the data table) L L L (place cursor in the L3 column) [ln] [data] / [data] ) [enter] [ nd ] [quit] [ nd ] [stat] [data] Æ (to highlight FORMULA) Data: (highlight L3) FRQ: (highlight one) [enter] (to obtain x ) x [enter] The result is [ nd ] [stat] 3 3 (to obtain Sx) Sx [enter] The result is Using the TI-30X IIS, the procedure is: [nd][stat] (Select -VAR) [DATA] [ENTER] X= ln(6/6) [ENTER] ØØ (Hit the down arrow twice) X= ln(56/6) [ENTER] ØØ X3= ln(64/56) [ENTER] ØØ X4= ln(59/64) [ENTER] ØØ X5= ln(63/59) [ENTER] ØØ X6= ln(64/63) [ENTER] [STATVAR] Æ Æ (Arrow over to Sx) [ENTER] (The result is ) ActuarialBrew.com 04 Page 5

16 [STATVAR] Æ (Arrow over to x ) [ENTER] (The result is ) To exit the statistics mode: [nd] [EXITSTAT] [ENTER] Alternatively, using the BA II Plus calculator, the procedure is: [nd][data] [nd][clr WORK] X0= 6/6 = LN [ENTER] ØØ (Hit the down arrow twice) X0= 56/6 = LN [ENTER] ØØ X03= 64/56 = LN [ENTER] ØØ X04= 59/64 = LN [ENTER] ØØ X05= 63/59 = LN [ENTER] ØØ X06= 64/63 = LN [ENTER] [nd][stat] ØØØ = (The result is ) [nd][stat] ØØ = (The result is ) To exit the statistics mode: [nd][quit] Therefore, the annualized estimates for the mean and standard deviation of the normal distribution are: r ˆ 0.5 ˆ h ˆ The estimate for the annualized expected return is: r ˆ ˆ a = + d + 0.5s = ( ) = h Solution 8 A Chapter 4, Utility Values and State Prices Since the probability of the high state is 0.60, the probability of the low state is: - p = = 0.40 The stock s cash flow in the low state can now be determined: dh dh S = QuSue + QdSde dh dh S = puusue + ( - pu ) dsde = e CLe CL = 8 ActuarialBrew.com 04 Page 6

17 The value of the derivative is: V(0) Q V (3) Q V (3) u u d d pu ln(30) ( p) U ln(8) u ln(30) ln(8).688 d Solution 9 E Chapter 8, Black-Derman-Toy Model The yield volatility for the 3-year bond is: s È -/( T -) -/ P(, T, ru) - ÈP(,3, ru) -, T = 0.5 ln Í = 0.5 ln Í -/( T -) -/ ÍÎP(, T, rd) - ÍÎP(,3, rd) - È -/ = Í = -/ ÍÎ ln 0.50 Solution 0 D Chapter, All-or-Nothing Options The trick to answering this question quickly is recognizing that d for Stock A is equal to d for Stock B: Stock A: Stock B: d d ( ) ln St / K + [ r - d s ]( T -t) = s T - t ln ( 75 / K ) + [ (0.) ]() = 0. ln ( 75 / K ) + [0.03]() = 0. ln ( St / K) + [ r -d -0.5 s ]( T -t) = s T - t ln ( 75 / K ) + [ (0.) ]() = 0. ln ( 75 / K ) + [0.03]() = 0. For Stock B, we can use the cash call price to determine Nd ( ): -rt ( -t) CashCall( K ) = e N( d ) -0.0() 0.39 = e N( d ) Nd ( ) = ActuarialBrew.com 04 Page 7

18 This value of Nd ( ) replaces Nd ( ) in the formula for the asset put on Stock A: -d ( T -t) AssetPut( K ) = Ste N( -d ) -0.09() = 75 e [ - N( d )] -0.09() = 75 e [ ] = 3.80 Solution B Chapter, Control Variate Estimate The payoff of an average strike Asian call option is the final stock price minus the average stock price, when that amount is greater than zero: Average strike Asian call option payoff = Max[ ST - S,0] These payoffs are shown in the rightmost columns below: i Arithmetic Average Geometric Average Final Stock Price 0.0 Ye i Arithmetic Option Payoff 0.0 Xe i Geometric Option Payoff The values in the two rightmost columns are the payoffs, which means that they are the rt discounted Monte Carlo prices, Y i and X i, times e. The estimate for b is: rt ( ) n n  i i  i i i= i= ( Y -Y)( X - X) e ( Y -Y)( X - X) b = = n n ( X - X) e ( X - X)  rt ( )  i i i= i= We get the same estimate for b regardless of whether we use the time 0 prices or the time payoffs (as shown in the rightmost expression above). To save time, we use the time payoffs from the table above. We perform a regression using the sixth column in the table above as the x-values and the fifth column as the y-values. The resulting slope coefficient is: b = During the exam, it is more efficient to let the calculator perform the regression and determine the slope coefficient. ActuarialBrew.com 04 Page 8

19 Using the TI-30XS Multiview calculator, we first clear the data by pressing [data] [data] until Clear ALL is shown, and then press [enter]. Fill out the table as shown below: L L L Next, press: [ nd ] [quit] (to exit the table) [ nd ] [stat] (i.e., select -Var Stats) Select L for x-data and press [enter]. Select L for y-data and press [enter]. Select CALC and then [enter] Exit the data table by pressing [ nd ] [quit]. Obtain access to the statistics by pressing [ nd ] [stat] 3 Note the following statistics: x 0.85 y 0 a (This is ) Alternatively, the TI-30X IIS or the BA II Plus can be used to obtain the values above. To use one of those calculators, follow the steps outlined at the end of this solution and then return to this point to continue the solution. The Monte Carlo estimate for the arithmetic average strike Asian put is: -rt ( -t) n e ( -0) A = Y = Â Vi ( T) = e [ 0] = n i = The Monte Carlo estimate for the geometric average strike Asian put is: rt ( t) n e 0.0 (0) G X Vi ( T) e n i The true price for the geometric option is $4.50, so the control variate price of the arithmetic average option is: A* = A + b ( G - G ) = ( ) = 4.94 ActuarialBrew.com 04 Page 9

20 Alternative Calculators Using the TI-30X IIS, the procedure is: [nd][stat] (Select -VAR) [ENTER] [DATA] X= 0.00 Ø (Hit the down arrow once) Y= 0.00 Ø X= Ø Y= 34.0 Ø X3= 6.00 Ø Y3= 5.80 Ø X4= 0.00 Ø Y4= 0.00 [ENTER] [STATVAR] Press the right arrow and note the following statistics: x 0.85 y 0 a (This is ) To exit the statistics mode: [nd] [EXITSTAT] [ENTER] Using the BA II Plus calculator, the procedure is: [nd][data] [nd][clr WORK] X0= 0.00 [ENTER] Ø (Hit the down arrow once) Y0= 0.00 [ENTER] Ø X0= [ENTER] Ø Y0= 34.0 [ENTER] Ø X03= 6.00 [ENTER] Ø Y03= 5.80 [ENTER] Ø X04= 0.00 [ENTER] Ø Y04= 0.00 [ENTER] [nd][stat] ActuarialBrew.com 04 Page 0

21 Press the down arrow and note the following statistics: x 0.85 y 0 b (This is ) To exit the statistics mode: [nd][quit] Solution B Chapters 3 & 8, Risk-Neutral Probability Let s use P(0,) to denote the price of a -year zero-coupon bond that matures for $. We can make use of put-call parity: C(90) 90 P(0,) S0 P(90) C(90) 90 P(0,) 80 P(90) C(90) P(90) P(0,) We can use the stock prices to determine the risk-neutral probability that the up state of the world occurs: ( r ) h h ( e d r0 ) d (.07) 40 / 80 p* 0.57 ud ud 0 / / 80 If the up state occurs, then the zero-coupon bond will have a value of at time, and.0 if the down state occurs, then the zero-coupon bond will have a value of at time..05 The time 0 value is found using the risk-neutral probabilities and the risk-free rate at time 0: P(0,) We can now use the equation for put-call parity described above to find the solution: C(90) P(90) P(0,) Solution 3 D Chapter 5, Partial Expectation The formula for the partial expectation is: ( )( Tt) PE S ˆ T ST K Ste N( d ) ( )3 PES3 S3 S0 S0e N( dˆ ) ActuarialBrew.com 04 Page

22 The values of ˆd and N( -d ˆ ) are: ÊS0 ˆ Á + a - d + s T - S 0 ln ( 0.5 )( t) ˆ Ë 0 + ( (0.5) )(3) d = = = s T - t N( - dˆ ) = N( ) = We can use the formula for the partial expectation to solve for the current stock price: ( )3 PE S3 S3 S0 S0e N( dˆ ) ( ) Se S Solution 4 E Chapter, Rolling Insurance Strategy The values of d and d for a 3-month put option with a strike price that is 95% of the current stock price are: ln( S/ 0.95 S) + ( r - d s ) T - ln(0.95) + ( )(0.5) d = = s T = d = d - s T = = From the normal distribution table: N( d ) N( ) N( d ) N( ) The cost of a 3-month put option that has a strike price of 95% of the current stock price is a function of the then-current stock price: rt T PEur ( S,0.95 S,0.5) 0.95 Se N( d) Se N( d) Se N( d) Se N( d) S 0.95 e ( ) S Therefore, the first put option can be purchased with shares of stock now, and the value of the first option is: P 0.045S F0,0( S) S (0) ActuarialBrew.com 04 Page

23 The second option can be purchased with shares of stock in 3 months. The current value of a share of stock 3 months from now is its prepaid forward price. The stock does not pay dividends, so the prepaid forward price is equal to the stock price, and the time 0 value of the second option is: P F0,0.5( S) = S(0) = = 4.5 The third option can be purchased with shares of stock in 6 months. The current value of a share of stock 6 months from now is its prepaid forward price, so the time 0 value of the third option is: P F0,0.5( S) = S(0) = = 4.5 The fourth option can be purchased with shares of stock in 9 months. The current value of a share of stock 9 months from now is its prepaid forward price, so the time 0 value of the fourth option is: P F0,0.75( S) = S(0) = = 4.5 Summing the prices of the four options, we have: = 6.46 Solution 5 C Chapter 4, Options on Futures Contracts Since the risk-neutral probability of an up move is equal to the risk-neutral probability of a down move, both probabilities are 50%: p* = - p* fi p * = 0.5 We are given that the ratio of the factors applicable to the futures price is: uf df = 3 ActuarialBrew.com 04 Page 3

24 The formula for the risk-neutral probability of an up move can be used to find u F and d F : - df p* = uf - df df - df df p* = uf df - df df - df = 3 - df uf = = df =. The tree of futures prices is therefore: Futures Prices The tree of prices for the European put option is: European Put The price of the European put is: e (/ )7.039 (/ ) The tree of prices for the American put option is: American Put If the futures price moves down to $96, then early exercise is optimal, as indicated above by the bolding for that node. ActuarialBrew.com 04 Page 4

25 The price of the American put is: e (/ )7.039 (/ ) The price of the American put option exceeds the price of the European put option by: Solution 6 A Chapter 5, Put-call Parity and S a Using the expected rate of price appreciation of % and the expected return of 5%, we can determine the dividend yield of the stock: 0. = a -d 0. = 0.5 -d d = 0.04 The price at time 0 of the contingent claim that pays [ S ()] 3 at time is: P r( T t) ( r) 0.5 ( ) ( Tt) F a tt, S( T) a a a a e S(0) e 0.0 ( 0) 3 3( ) 0.53(3)0.30 (0) 0.35 e e 8e.355 The usual expression for put-call parity is: -rt P C + Ke = F0, T ( S) + P In this case, the underlying asset is 3 -rt P 3 C + K e = F0, T ( S ) + P P 3 3 -rt C - P = F0, T ( S )- K e C - P = e C - P = S and the strike asset is 3 K : The cost of establishing the position consisting of a long call and a short put is.978. Solution 7 C Chapter 9, Risk-Neutral Version of the Vasicek Model The process for the short rate follows the Vasicek Model. The true process can be rewritten in the familiar form: dr 0.06(0. r) dt 0.07 dz a 0.06, b 0., 0.07 ActuarialBrew.com 04 Page 5

26 We can use (iii) to obtain the Sharpe ratio: Zt () = Zt ()-ft Z (5) = Z(5) -5f = 0.4-5f f = 0.06 The parameter B (5,0) is: a( Tt) e BtT (, ) a a(0 5) e e B(5,0) a 0.06 We can use the Sharpe ratio to determine a(0.09,5,0) : a(,, rtt) - r f( rt, ) = qrtt (,, ) a( rtt,, )- r f = BtT (, ) s a(,, rtt) = r+ BtT (, ) sf a(0.09,5,0) = = 0.08 Solution 8 E Chapter 3, Alternative Binomial Trees If the option has a positive payoff in both the up and down states, then: -d h Vu - Vd (53 -Su) -(53 -Sd) Sd -Su D= e = e = e = S( u-d) Su-Sd Su-Sd But D=-0.64, so the option must have a zero payoff in one of the two states. The payoff is clearly positive if the stock price is , so the payoff must be zero in the other state. For a put option, the positive payoff occurs in the low state, suggesting that Sd = and Su > 53. We can use D to solve for Su : = D -d h Vu - Vd = e Su - Sd ( ) = e Su Su = ActuarialBrew.com 04 Page 6

27 The standard binomial model, the Cox-Ross-Rubinstein model and the Jarrow-Rudd model all have the same ratio of u to d: u s = e h d Therefore, the ratio of Su to Sd can be used to obtain s : Su u = Sd d Su s h = e Sd s 0.5 = e = s Solution 9 A Chapter 5, Covariance of S t and S T To answer this question, we use the following formulas: ÈST = ( a -d)( T -t) EÍ e Î St È ( a -d)( T -t) Ê s ( T -t) Var = - ˆ ÎST St St e e Ë ÈST Cov[ St, ST ] = E Í Var È ÎSt S0 Î St The variance of X is: ( ) [ ] Var ÈÎX S(0) = Var È Î4 S() - S(3) = Var 8 S() -4 S(3) = 64 VarS [ ()] + 6 VarS [ (3)] + 8 (-4) CovS [ (), S(3)] The variances of S () and S (3) are: È ( )(-0) Ê 0. (-0) Var = - ˆ ÎS S0 4 e e = Ë È ( )(3-0) Ê 0. (3-0) Var = - ˆ ÎS3 S0 4 e e = Ë The covariance is: ÈS3 È ( )(3-) Cov[ S, S3] = E Í Var ÎS S0 = e = ÎS ActuarialBrew.com 04 Page 7

28 We can now find the variance of X : Var ÈÎX S(0) = 64 Var[ S()] + 6 Var[ S(3)] + 8 (-4) Cov[ S(), S(3)] = (- 4) = Solution 30 D Chapter, Stratified Sampling Method The stratified sampling method assigns the first, fifth, and ninth uniform (0, ) random numbers to the segment (0.00, 0.5), the second, sixth and tenth uniform (0, ) random variables to the segment (0.5, 0.50), and the third, seventh and eleventh uniform (0, ) random variables to the segment (0.50, 0.75), the fourth, eighth and the twelfth uniform (0, ) random variables to the segment (0.75,.00). The lowest simulated normal random variables will come from the segment (0.00, 0.5). The lower of the three values in this segment is the ninth one: Min [ 0.540,0.30,0.44] = 0.44 Therefore, we use 0.44 to find the lowest standard normal random variable and the lowest stock price: u9 = [(9 - )mod 4] uˆ 9 = V9 = = = Z6 = N (0.0600) = ( a-d s ) T+ sz T ( (0.5) ) + 0.5( ) ST ( ) = S0e = 0e = 7.44 The highest simulated normal random variable will come from the segment (0.75,.00). The highest of the three values in this segment is the eighth one: Max [ 0.450,0.909,0.50] = Therefore, we use to find the highest standard normal random variable and the highest stock price: u8 = [(8 - )mod 4] uˆ 8 = V8 = = = Z8 = N (0.9775) = ( a-d s ) T+ sz T ( (0.5) ) + 0.5(.00000) ST ( ) = S0e = 0e = The difference between the largest and smallest simulated stock prices is: = ActuarialBrew.com 04 Page 8