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Can you please explain Why P(W2) is 4/9 ? Thanks.. enter image description here

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This is because you are searching for the white marbles and there are total 4 white marbles. And the total marbles you've got is 9. So it 4/9.

You don't actually need this method, You just need the probability of the second draw.Because the second draw is without replacement, Total marbles decrease by 1 and now the total is 8, because already a white marble is taken, total no. of white marbles left is 3. So the answer is 3/8. Easy...comment if there is any doubt.

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  • $\begingroup$ But this is without replacement..so shouldn't we be choosing from a total of 8 on the second draw? $\endgroup$ – Memo Jun 10 '14 at 15:44
  • $\begingroup$ edited...@Memo check it out! $\endgroup$ – Kiara Jun 10 '14 at 15:47
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    $\begingroup$ Yes the book this is from has Method 2 like you said..I just wanted to also understand the first method.Thanks. $\endgroup$ – Memo Jun 10 '14 at 15:47
  • $\begingroup$ you have to justify that the result remain true for the 2nd marble as well as for the first... $\endgroup$ – mookid Jun 10 '14 at 16:06

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