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June 11th, 2011, 08:20 AM  #1 
Senior Member Joined: Mar 2011 Posts: 105 Thanks: 0  Probablity !!!! Confusing
10 black, 20 white, 40 red The question is what is probability when we reach 5 of them, and we have 2 white, 2 red, 1 black....... And some guy solved this question on youtube, and his answer was 12.2% He solve like : (20C2 x 40C2 x 10C1)/ (70C5) YouTube  ‪Probability  Hard (Part 1)‬‏ I know he was right. BUt I don't understand it I solve by another way like : Doing it your way, you would calculate the probability for each of the 30 possible ways to draw 2W, 2R and one B. So, to draw WWRRB in that order, you get (20/70)(19/69)(40/6(39/67)(10/66) Each iteration of 2W, 2R, and 1B has an identical probability. So, multiply by 30, and you get 12.2%. Can somebody explain me about first way? I really can't make sense!! i KNOW WHAT 70c5 MEAN..... my ways, and his way 's so different..... It's not related with his way.... BUt it comes out same answer 
June 11th, 2011, 11:19 AM  #2  
Math Team Joined: Dec 2006 From: Lexington, MA Posts: 3,267 Thanks: 407  Re: Probablity !!!! Confusing Hello, daivinhtran! Quote:
He reasoned it out like this . . . [color=beige]. . [/color] We want 2 White from the available 20 Whites. [color=beige]. . [/color] We want 2 Red from the available 40 Reds. [color=beige]. . [/color] We want 1 Black from the available 10 Blacks. [color=beige]. . [/color]  
June 11th, 2011, 06:58 PM  #3  
Senior Member Joined: Mar 2011 Posts: 105 Thanks: 0  Re: Probablity !!!! Confusing Quote:
I can't make sense how related them are......  
June 11th, 2011, 09:11 PM  #4 
Senior Member Joined: Apr 2011 From: USA Posts: 782 Thanks: 1  Re: Probablity !!!! Confusing
WOW. This is the THIRD posting of this same problem. I've stopped attempting to read it cause I don't feel like jumping back and forth from thread to thread to get all the various pieces. Have you EVER thought to post again on your same thread so that everything is in one place, so as not to confuse everyone? Sigh. 
June 12th, 2011, 12:49 AM  #5  
Senior Member Joined: Sep 2010 Posts: 101 Thanks: 0  Re: Probablity !!!! Confusing Quote:
 

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