From: h.jurjus@hetnet.nl   
      
   "Andrew Au Ying Hung"  wrote in message news:bmi1   
   5$i3q$1@mulga.cs.mu.OZ.AU...   
   > Dear all,   
   >   
   >     Here is a simple question of probability that I tried hard for a half   
   > day with no result.   
   >   
   > Given a game of tossing coin, not until the recent three tosses have exactly   
   > two heads up, I will keep tossing.   
   > What is the expectation of the number of toss I have the made?   
   >   
   >     The problem looks simple, but it turns out quite hard to solve, at   
   > least, for me. Please spend a little time to try it out ^^   
      
   Have you tried sci.math?   
      
   Cheers,   
   Herman Jurjus   
      
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