http://www.cut-the-knot.org/Probability/Expectation.shtml [2]
http://www.cut-the-knot.org/Probability/TennisClub.shtml [3]
http://www.cut-the-knot.org/Probability/LengthToFirstSuccess.shtml [4]
Links[1] https://www.hootsgo.org/?q=node/6721 [2] http://www.cut-the-knot.org/Probability/Expectation.shtml [3] http://www.cut-the-knot.org/Probability/TennisClub.shtml [4] http://www.cut-the-knot.org/Probability/LengthToFirstSuccess.shtml
