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June 6th, 2011, 01:09 PM  #1 
Newbie Joined: Jun 2011 Posts: 1 Thanks: 0  Probability question =.=
need help on this one: box # 1 contains 1 purple and 2 pink marbles. box # 2 contains 2 purple and 1 pink marbles. a marble is chosen at random from box #2 and placed in box #1. find the probability of now choosing a pink marble from box #1. so far I think i go with P(box#1/pink) = P(box#1 and pink)/P(pink) using the formula P(E/F)=P(E and F)/P(F) where E represents the location and F represents the item 
June 6th, 2011, 03:06 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,822 Thanks: 723  Re: Probability question =.=
I suggest that instead of using formulas mechanically, you try to see what is going on. Step 1: prob(purple is chosen = 2/3, prob (pink is chosen) = 1/3. Step 2: purple chosen in step 1, then prob(pink chosen) = 1/2; pink chosen in step 1, then prob(pink chosen) = 3/4. Put it all together prob(pink in step 2) = 2/3 x 1/2 + 1/3 x 3/4 = 7/12. 
June 6th, 2011, 08:22 PM  #3 
Senior Member Joined: Apr 2007 Posts: 2,140 Thanks: 0 
Steps 1 and 2 given by mathman are correct.

June 6th, 2011, 11:14 PM  #4  
Member Joined: May 2011 Posts: 51 Thanks: 0  Re: Probability question =.= Quote:
 

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