Value a Die Game with Optional Continuation
Company: Squarepoint
Role: Quantitative Researcher
Category: Statistics & Math
Difficulty: medium
Interview Round: Technical Screen
You repeatedly roll a fair six-sided die. You always collect the number rolled. If the roll is 1 or 2, the game ends immediately. If the roll is 3, 4, 5, or 6, you may either stop with your accumulated winnings or continue rolling.
Assuming risk-neutral preferences and no discounting, what is the fair price of the game and what is the optimal stopping policy? Derive the value rather than estimating it by simulation.
### Constraints & Assumptions
- Winnings accumulate across rolls.
- The decision to continue is made after collecting a 3, 4, 5, or 6.
- There is no fixed horizon, transaction cost, or loss on a later roll.
- “Fair price” means expected monetary value to a risk-neutral player.
### Clarifying Questions to Ask
- Are the amounts accumulated or does only the final roll pay?
- Is stopping allowed after a 1 or 2, or is termination forced?
- Does continuing ever forfeit prior winnings?
- Is the player risk neutral?
```hint Write a continuation-value equation
After any optional stopping point, the future game has the same value as it did before the first roll.
```
### What a Strong Answer Covers
- A Bellman or first-step equation for the continuation value.
- Justification that continuing after 3 through 6 is optimal.
- The numerical expected value and a distinction between fair value and personal willingness to pay.
- A check that the expected game length is finite.
### Follow-up Questions
- How would a per-roll fee change the stopping decision?
- What if a later roll of 1 or 2 erased all accumulated winnings?
- How would risk aversion affect the maximum entry price?
Overview: Value an infinite-horizon die game with optional continuation. Derive the Bellman equation, optimal always-continue policy, expected entry value, and the role of risk preferences.
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