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May 18th, 2009, 11:08 AM  #1 
Newbie Joined: May 2009 Posts: 15 Thanks: 0  Help with Probability Can someone please look over the small chart I made that describes the probability game I made up and tell me if it's correct? In my game, the player picks three cards from a deck, placing each one to the side as they are chosen. If all three cards are the same colour, they win a certain amount of money. If the cards are any other combinatrion of red and black, they win nothing. P(x) is probability, and ? XP(x) is the expected winnings on average. Does this make sense? Please help! 
May 18th, 2009, 04:45 PM  #2  
Global Moderator Joined: May 2007 Posts: 6,684 Thanks: 658  Re: Help with Probability Quote:
What is x? You have defined it to mean 3 red cards, 3 black cards, or either event?  
May 19th, 2009, 06:22 AM  #3 
Newbie Joined: May 2009 Posts: 15 Thanks: 0  Re: Help with Probability
X is the amount of money the player wins if they get three red or three black cards.

May 20th, 2009, 05:09 PM  #4 
Global Moderator Joined: May 2007 Posts: 6,684 Thanks: 658  Re: Help with Probability
Your calculation of expected return on a bet is correct, although to be fair you need to subtract the cost of the bet.

May 23rd, 2009, 02:42 AM  #5 
Global Moderator Joined: Dec 2006 Posts: 20,281 Thanks: 1965 
The probability that the second and third cards match the first is (25/51)(24/50), i.e., 4/17, so the expected return is 28/17. You don't need a chart for that and don't need to calculate anything to nine decimal places.


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