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May 19th, 2017, 12:38 AM  #1 
Newbie Joined: May 2017 From: sweden Posts: 1 Thanks: 0  Bags problem
You have 2 bags, A and B In bag A there's 3 white balls and 2 black balls In bag B there's 1 white balls and 3 black balls If you take only one ball from each bag, what is the probability that you will get one white ball and one black ball? Remember that there are two different combinations: A:3/5 and 3/4 = 45% B:1/4 and 2/5 = 10% Is the answer the average of 45 and 10 or are you supposed to just add them up? 
May 19th, 2017, 04:06 AM  #2 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 12,623 Thanks: 845 
b,w : 2/5 * 1/4 = 2/20 w,b : 3/5 * 3/4 = 9/20 add 'em: 11/20 multiply 'em: 18/400 = 9/200 SO? 
May 19th, 2017, 04:03 PM  #3 
Senior Member Joined: Sep 2015 From: USA Posts: 1,981 Thanks: 1027 
to be formal it's $p = \dfrac{\dbinom{3}{1}}{\dbinom{5}{1}} \dfrac{\dbinom{3}{1}}{\dbinom{4}{1}}+\dfrac{ \dbinom{1}{1}}{\dbinom{4}{1}} \dfrac{\dbinom{2}{1}}{\dbinom{5}{1}}=\dfrac{11}{20 }$ 
May 19th, 2017, 05:13 PM  #4 
Senior Member Joined: Feb 2016 From: Australia Posts: 1,597 Thanks: 546 Math Focus: Yet to find out. 
Bags bags bags.. they're very useful things..


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