1. A player throws a fair coin and wins $1 each time it's heads, but loses $1 each time it's tails. The player will stop when his or her net winnings reach $1, or after n throws, whichever comes sooner. What is the player's probability of winning, and expected loss conditional on not winning, if (a) n = 3? (b) n = 5?
2. Let α be a stopping time and τ (n) a nondecreasing sequence of bounded stopping times, both for a martingale {Xn, Bn }n≥1. Show that α is also a stopping time for the martingale {Xτ (n), Bτ (n)}n≥1, in the sense that {α ≤ τ (n)}∈ Bτ (n) for each n.