Markets: A Rigorous Course

M03 · Problem 3 ★★ Check

Kelly versus expected wealth

(a) Prove Proposition 3.3(b): for any fixed f≠f∗f \ne f^* in [0,1)[0, 1), Wn(f∗)/Wn(f)→∞W_n(f^*)/W_n(f) \to \infty almost surely. (b) For p=0.55p = 0.55, b=1b = 1, n=10n = 10: compute E[W10]/W0E[W_{10}]/W_0 and P(W10>0)P(W_{10} > 0) for f=1f = 1, and E[W10]/W0E[W_{10}]/W_0 and the median of W10/W0W_{10}/W_0 for f=f∗f = f^*. (c) Explain in two sentences why maximising expected wealth is the wrong objective for a trader who bets repeatedly.

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