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Probability_independent [#permalink] New post 03 Sep 2007, 01:21
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 [#permalink] New post 03 Sep 2007, 01:41
St1:
P(A) = 0.25. But we do not know P(B). Insufficient.

St2:
P(!B) = 0.71. But we do not know anything about P(A). Insufficient.

Using both, we know P(A) = 0.25, P(B) = 1-0.71 = 0.29. So we can calculate P(A) * P(B) and determine if it is greater than 0.3.

Ans C
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 [#permalink] New post 03 Sep 2007, 10:38
Probability P(A and B) for independen events A and B is P(A).P(B)

1st condition.... P(A) = 0.25.
Since P(B) <1 so P(A).P(B) <0.3 SUFFICIENT

2nd condition .... P(B) = 1-0.71 = 0.29
Since P(A) <1 so P(A).P(B) < 0.3 SUFFICIENT

So each alone is sufficient. (D) is correct.
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 [#permalink] New post 03 Sep 2007, 22:28
I got into trap and answered C (the same method as ywilfred)

zzyyxx: Thanks a lot!
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 [#permalink] New post 03 Sep 2007, 22:37
zzyyxx wrote:
Probability P(A and B) for independen events A and B is P(A).P(B)

1st condition.... P(A) = 0.25.
Since P(B) <1 so P(A).P(B) <0.3 SUFFICIENT

2nd condition .... P(B) = 1-0.71 = 0.29
Since P(A) <1 so P(A).P(B) < 0.3 SUFFICIENT

So each alone is sufficient. (D) is correct.


Thanks! that question is tricky
  [#permalink] 03 Sep 2007, 22:37
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