Suppose you know beforehand that in one of the envelopes there are 10 bucks and in the other envelope there are 20 bucks.
When you pick up your first envelope, your expectation would be
Similarly, when you are going to pich up the second envelope, you know either it contains 10 bucks or 20 bucks.
Hence your expectataion would be
Now suppose that you are again beginning the game and you don't know how many bucks are kept inside the envelopes(in the first case you were told 10 and 20 bucks)
You picked up one envelope and called this amount A.
Now, there are two possibilities:initially the amount ia A& A/2 or A&2A.Hence the expection would be:
Your expectation changes with your knowledge about the envelopes.
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