Each day Donna and Mary toss a coin to see who buys the other person coffee ($2.34 a cup). One tosses and the other calls the outcome. If the person who calls the outcome is correct, the other buys the coffee; otherwise the caller pays. Assume that an honest coin is used, that Mary tosses the coin, and that Donna calls the outcome. Find Mary's expected payback. Is this a fair game?
Now how much is she expected to pay back?