Library/CFA (Chartered Financial Analyst)/Derivatives (CFA Program Curriculum 2026 • Level I • Volume 7)/Learning Module 10 Valuing a Derivative Using a One-Period Binomial Model

Learning Module 10 Valuing a Derivative Using a One-Period Binomial Model

45 questions available

Binomial framework and hedge replication5 min
The one-period binomial model assumes that over one period the underlying asset price will move either up to S1_u or down to S1_d. Define Ru = S1_u / S0 and Rd = S1_d / S0. Options have asymmetric payoffs and therefore require modeling future price behavior; forwards have symmetric payoffs and can be priced without modeling. In the binomial approach, form a portfolio by selling (or buying) one option and taking a position h in the underlying such that the portfolio's payoff is identical in the up and down states. Solve h via h = (c1_u - c1_d) / (S1_u - S1_d) for a call (or analogous formula for a put), which is the hedge ratio. With the hedged portfolio payoff equal in both states, that certain payoff must earn the risk-free rate; discount the known payoff to obtain the option price: c0 = h S0 - V1 / (1 + r) where V1 is the common payoff. Equivalently, define the risk-neutral probability pi = (1 + r - Rd) / (Ru - Rd). The option price equals the discounted risk-neutral expected payoff: c0 = [pi c1_u + (1 - pi) c1_d] / (1 + r). Actual (real-world) probabilities or investors' risk aversion do not enter the no-arbitrage price; only Ru, Rd (which capture volatility) and the risk-free rate matter. The one-period model generalizes to multi-period trees by iterating the same steps. Practical examples compute hedge ratios and option prices numerically and show consistency with put-call parity in deriving related put values. The law of one price underpins the method: two portfolios with identical payoffs at expiration must have equal prices today or arbitrage exists.

Key Points

  • Underlying moves only to two possible prices: S1_u or S1_d
  • Hedge ratio h = (option up payoff - option down payoff) / (S1_u - S1_d)
  • Hedged portfolio payoff is risk-free and must earn risk-free rate
  • Option price from replication: discount the certain payoff
  • Model depends on Ru and Rd (volatility) and risk-free rate, not real-world probabilities
Risk-neutral probabilities and implications5 min
The one-period binomial model assumes that over one period the underlying asset price will move either up to S1_u or down to S1_d. Define Ru = S1_u / S0 and Rd = S1_d / S0. Options have asymmetric payoffs and therefore require modeling future price behavior; forwards have symmetric payoffs and can be priced without modeling. In the binomial approach, form a portfolio by selling (or buying) one option and taking a position h in the underlying such that the portfolio's payoff is identical in the up and down states. Solve h via h = (c1_u - c1_d) / (S1_u - S1_d) for a call (or analogous formula for a put), which is the hedge ratio. With the hedged portfolio payoff equal in both states, that certain payoff must earn the risk-free rate; discount the known payoff to obtain the option price: c0 = h S0 - V1 / (1 + r) where V1 is the common payoff. Equivalently, define the risk-neutral probability pi = (1 + r - Rd) / (Ru - Rd). The option price equals the discounted risk-neutral expected payoff: c0 = [pi c1_u + (1 - pi) c1_d] / (1 + r). Actual (real-world) probabilities or investors' risk aversion do not enter the no-arbitrage price; only Ru, Rd (which capture volatility) and the risk-free rate matter. The one-period model generalizes to multi-period trees by iterating the same steps. Practical examples compute hedge ratios and option prices numerically and show consistency with put-call parity in deriving related put values. The law of one price underpins the method: two portfolios with identical payoffs at expiration must have equal prices today or arbitrage exists.

Key Points

  • Risk-neutral probability pi = (1 + r - Rd) / (Ru - Rd)
  • Option price = discounted risk-neutral expected payoff
  • Real-world probabilities do not affect no-arbitrage price
  • Higher Ru - Rd (volatility) increases option prices
  • Risk-free rate shifts influence put and call differently through discounting and pi
Examples, put-call parity consistency, and extensions5 min
The one-period binomial model assumes that over one period the underlying asset price will move either up to S1_u or down to S1_d. Define Ru = S1_u / S0 and Rd = S1_d / S0. Options have asymmetric payoffs and therefore require modeling future price behavior; forwards have symmetric payoffs and can be priced without modeling. In the binomial approach, form a portfolio by selling (or buying) one option and taking a position h in the underlying such that the portfolio's payoff is identical in the up and down states. Solve h via h = (c1_u - c1_d) / (S1_u - S1_d) for a call (or analogous formula for a put), which is the hedge ratio. With the hedged portfolio payoff equal in both states, that certain payoff must earn the risk-free rate; discount the known payoff to obtain the option price: c0 = h S0 - V1 / (1 + r) where V1 is the common payoff. Equivalently, define the risk-neutral probability pi = (1 + r - Rd) / (Ru - Rd). The option price equals the discounted risk-neutral expected payoff: c0 = [pi c1_u + (1 - pi) c1_d] / (1 + r). Actual (real-world) probabilities or investors' risk aversion do not enter the no-arbitrage price; only Ru, Rd (which capture volatility) and the risk-free rate matter. The one-period model generalizes to multi-period trees by iterating the same steps. Practical examples compute hedge ratios and option prices numerically and show consistency with put-call parity in deriving related put values. The law of one price underpins the method: two portfolios with identical payoffs at expiration must have equal prices today or arbitrage exists.

Key Points

  • Numeric examples show hedge ratio and option price computation
  • Put prices derived from call prices via put-call parity remain consistent with binomial valuation
  • Arbitrage arises if market option prices deviate from no-arbitrage values
  • Method extends to multi-period binomial trees
  • Firm-value and other conceptual applications connect option views to balance-sheet claims

Questions

Question 1

In a one-period binomial model the underlying price S0 = 50. After the period it will be either S1_u = 65 or S1_d = 40. A European call with strike X = 55 expires at period end. If the risk-free rate for the period is 2 percent, what is the hedge ratio h for a short call position replicated by buying h units of the underlying?

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Question 2

A stock S0 = 80 will be either 110 (up) or 60 (down) next period. A call with X = 100 has payoffs 10 and 0 in the states. If r = 5 percent, what is the risk-neutral probability pi of an up move?

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Question 3

True or false: In the one-period binomial model, the actual real-world probability q of an up move affects the no-arbitrage option price.

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Question 4

Stock S0 = 100 is expected to go to either 130 or 70. Consider a put with X = 90 and r = 0. What is the put payoff vector (p1_u, p1_d)?

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Question 5

A put's payoffs are (0, 20) as in Question 5. With pi = 0.58333 and r = 5 percent, what is the put price p0?

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Question 6

Which of the following statements best describes why put and call prices derived from the one-period binomial model do not require investors' risk preferences?

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Question 7

Stock S0 = 16 moves to either 20 or 12. If r = 5 percent, what is the risk-neutral probability pi?

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Question 8

In a one-period model, increasing the spread between Ru and Rd while keeping S0 and r fixed will generally:

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Question 9

You sell a call and buy h units of the underlying to form a risk-free portfolio. If V1 is the common payoff in both states and r is the period rate, which equation gives c0 (call price)?

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Question 10

If a call option is overpriced relative to the binomial no-arbitrage price, an arbitrageur should:

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Question 11

Which of the following is a correct expression of the hedge ratio for any derivative whose value at expiry depends only on the underlying price in the two states?

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Question 12

Given S0 = 120, S1_u = 150, S1_d = 90, X = 110, r = 4 percent. A call's payoffs are (40, 0). Compute c0 using risk-neutral pricing.

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Question 13

If the risk-free rate increases while Ru and Rd remain unchanged, which of the following is typically true for European calls and puts (other things equal)?

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Question 14

A derivative has payoffs c1_u = 30 and c1_d = 5. Under S1_u = 150 and S1_d = 100 and S0 = 120, what is the hedge ratio h?

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Question 15

Which of the following best explains why replication pricing yields the same option price as discounted risk-neutral expected payoff?

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Question 16

If a one-period binomial model gives h = 0.2 and S0 = 80 and the common payoff V1 = 12 with r = 5 percent, what is the call price c0?

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Question 17

A European call in a one-period model has c1_u = 12 and c1_d = 0. If S1_u = 132, S1_d = 88 and S0 = 110, what is h?

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Question 18

Which factors determine the risk-neutral probability pi in a one-period binomial model?

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Question 19

Consider S0 = 300, S1_u = 360, S1_d = 240, X = 320, r = 0. What is the call's up and down payoff vector (c1_u, c1_d)?

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Question 20

If the hedged portfolio yields V1 = 50 in both states and r = 10 percent, what is present value V0 used in replication pricing?

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Question 21

A trader constructs a synthetic long underlying by combining a long call, short put (same X and T) and lending PV(X). Which parity principle justifies this?

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Question 22

In a one-period binomial model, if S0 = 50, Ru = 1.4, Rd = 0.8, and r = 5 percent, what is Ru - Rd?

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Question 23

Which of the following is NOT required to compute the no-arbitrage price of a European option in a one-period binomial model?

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Question 24

You observe a call priced below its binomial no-arbitrage value. Arbitrage strategy to exploit this mispricing is to:

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Question 25

A one-period call has c1_u = 8, c1_d = 1. Under S1_u = 120, S1_d = 80, S0 = 100, r = 2 percent. What is the hedge ratio h?

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Question 26

Which statement about multi-period extension of the one-period binomial model is correct?

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Question 27

When forming a hedged portfolio by selling one call and buying h shares, the portfolio is risk-free because:

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Question 28

If a put is overpriced in the market relative to its binomial no-arbitrage price, an arbitrageur should:

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Question 29

Which of the following increases the risk-neutral probability pi for an up move, holding Ru and Rd constant?

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Question 30

Why does increasing Ru and decreasing Rd (wider up/down moves) raise both call and put prices?

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Question 31

A protective put portfolio equals which of the following at inception according to put-call parity?

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Question 32

If S0 + p0 > c0 + PV(X) in the market, an arbitrageur should:

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Question 33

A stock S0 = 295, forward price F0(T) = 300.84, r and T such that PV(X)=295. Which statement about a call and put with X = F0(T) is correct today?

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Question 34

You calculate a put price via binomial model as 6.20. Market put trades at 7.00. Which elementary arbitrage is suggested by the chapter?

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Question 35

Which statement about the hedge ratio h is correct as option goes deeper in-the-money (all else equal)?

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Question 36

Given S0 = 50, S1_u = 75, S1_d = 25, a call with X = 60 has payoffs (15, 0). If r = 0 and you short the call and buy h underlying to hedge, what is V1 (common payoff) you will obtain?

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Question 37

If option c0 equals 4.57 as earlier example and S0 = 80, h = 0.2, what is current value of hedged portfolio V0?

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Question 38

A one-period model yields pi = 0.48. Option payoffs are c1_u = 10 and c1_d = 0. With r = 5 percent, what is c0?

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Question 39

A stock pays no dividends. If you observe a call and put with same X and T, which parity holds that links calls, puts, underlying, and bond?

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Question 40

A trader wants to replicate a sold call when exercise is certain at maturity. Which replication matches the sold-call payoff according to the chapter?

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Question 41

You price a call using replication and obtain c0 = 5.00. Using put-call parity with S0 = 50 and PV(X) = 45, what should the put p0 equal?

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Question 42

If an option's time-to-expiration shortens (T decreases) while other inputs unchanged, what is the typical effect on option time value?

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Question 43

A bank observes a one-period call price computed as 6 by the binomial model but market call is 8. If frictionless trading is possible, net initial cash flow from arbitrage by following correct strategy?

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Question 44

Which of the following best describes why both put and call premiums increase when volatility rises (holding other inputs constant)?

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Question 45

In the one-period binomial model, which of the following reasons explains why the underlying's expected return mu does not affect option price?

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