Consider the random variable: Where each Bi is obtained as a result of the toss of a

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Consider the random variable:

image

Where each Bi is obtained as a result of the toss of a fair coin:

image

We let n = 4 and consider X4.

(a) Calculate the E [X4| I1], E [X4| I2], E [X4| I4]

(b) Let

Zi = E [X4| Ii]

Is Zi, I = 1. . . 4, a martingale?

(c) Now define:

Vi = Bi + ?i

And

Is Vi a martingale?(d) Can you convert Vi into a martingale by an appropriate transformation?(e) Can you convert Vi into a martingale by changing the probabilities associated with a cointoss?

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