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June 6th, 2011, 01:09 PM   #1
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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
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June 6th, 2011, 03:06 PM   #2
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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.
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June 6th, 2011, 08:22 PM   #3
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Steps 1 and 2 given by mathman are correct.
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June 6th, 2011, 11:14 PM   #4
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Re: Probability question =.=

Quote:
Originally Posted by mathman
I suggest that instead of using formulas mechanically, you try to see what is going on.
+1, every formula is derived from the concept for user-friendly. Once you understand, it will be a pleasure.
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