Hi Mario, If I understand your problem statement, the random choice of one of the two envelopes ensures that the probability of choosing one or the other is 0.5. If you find 10 (units, I can't find the pound symbol on this keyboard), there is an equal likelihood that the other envelope contains 5 or 20 units. Your expected value for the swap is thus 7.5*0.5 + 15*0.5 = 11.25 units. The trick is in the "twice as much, half as much" statement. If it was x units more or less, a symmetric distribution, swapping wouldn't make any difference.
Jim ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
